Huh jshore, I thought you were the one who said that!
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(AND happy birthday : )
Although I would like to steal credit for it, it was Bill! (And, thanks!)
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I think the answer to the OP got lost in the shuffle. Baker, who’s a professional, got it right in post #23.
I compared recipes for banana cake and banana bread. There are distinct differences: Banana bread contains fewer eggs, less butter, and less liquid. Thus quick breads are by nature denser than cakes. They are not merely cake in a loaf form.
Similarly, muffins, which are simply small quick breads, are denser than cupcakes.
The Finns? Traditionally known as Pulla, for anyone interested in looking up other recipes.
It’s not the frosting, because there are cakes without frosting (pound cake and some coffee cakes , for example). I think it’s got more to do with how and when it is served - I’ve never seen banana bread on a dessert menu or served at a birthday party, while I’ve seen carrot cake in both situations. Banana bread seems to be more of a breakfast/coffee break/sandwich sort of food. Searching for “banana bread sandwich” got me grilled cheese sandwiches and pulled pork sandwiches, in addition to the peanut butter/cream cheese sandwiches I expected. " Carrot cake sandwich" got me carrot cake sandwich cookies.
Reminds me of when I had a huckleberry soda (artificially flavored). Now, for naturally-flavored sodas, the distinction between “huckleberry” and “blueberry” would be obvious: It’d be what kind of berry you did, in fact, add to the recipe. But what’s the difference between artificial huckleberry flavor and artificial blueberry flavor?
For me, that’s the main difference. Carrot cake you have to eat with a fork; banana bread and zucchini bread you can eat with your fingers. At least how I’ve always had it. The crumb on carrot cake is much airier than banana or zucchini bread.
But it’s not so cut & dried. “Tradition” or “alliteration” is as good as an answer as any for me. Why is cheesecake a cake but pumpkin pie is a pie? There’s a Polish apple pastry called szarlotka that gets translated as either “Polish apple pie” or “Polish apple cake” depending on who is doing the translation (to me, it’s more the latter, or perhaps even a torte, depending on your taxonomy of pastries.)
But with that, wouldn’t you have guessed that the carrot baked good would pair more logically with “bread” and bananas with “cake” without even contemplating where zucchini goes?
No.
It would go the other direction. Not anchoring to its origin, but framed relative to its origin. Sweet in the universe of vegetable based products vs savory in the universe of fruit based ones.
That said I think the true answer is more history.
Carrot cake was popularized as a cake to be served as a cake in the UK during WWII due to shortages of fruits otherwise used in cake products. It was “sold” as a dessert that could be made with what was more available. It could make a cake with less added sugar. You don’t usually serve bread for dessert after dinner.
Bananas though were mainly thought of as a breakfast food. What to do with them when they got over ripe? It was the ‘30s. You can’t waste them! Answer - cook it in a quick bread, still for breakfast, not a dessert after dinner. Yes you can serve a coffee cake with breakfast, so you can have cake with breakfast, but not typically. And the original banana breads had little added sugar and extra bran added as a cheap filler.
The sweeter moister product we now think of as banana bread didn’t appear as a modification of the product until the late ‘60s into the ‘70s.
While we’re at it, what’s up with yellowcake and urinal cake?
Agree with this.
Anyone want my durian doughnut recipe?
mmm
I guess it means there’s no real difference between cake and bread, and the naming is completely arbitrary based on how alliterative it is. Makes perfect sense to me.
Well, I wouldn’t say it’s completely arbitrary. There are some things that are unambiguously bread rather than cake, and some things that are unambiguously cake rather than bread, with a multi-axis continuum of things in between.
Personally, if I were creating the language from scratch, I think I’d put the dividing line at dough vs. batter. But even there, there are going to be ambiguous cases: What’s the difference between a very soft dough and a very thick batter? And that would also leave open the possibility of sugar-free cakes, and breads loaded with sugar.
Banana bread has always seemed breadier to me than carrot cake (that density thing again), and I’ve never seen a frosted banana bread, which might confuse the issue.
Otherwise, you might as well ask why we drive on a parkway but park in a driveway.
Just because it’s called Banana Bread doesn’t mean it’s “considered a bread”. Jellyfish are not considered to be fish, and seahorses aren’t considered to be horses. I’m not saying it isn’t considered a bread, just that the name alone is insufficient evidence.
I for one would not put it in the category bread, but I come from a different culture. The general category of “bread” is, as far as I can tell, more narrow in Norway. That’s not obvious from naming things though. While what gets labeled “Norwegian Christmas bread” by recipe sites is called “Yule cake” (Julekake) in Norwegian, the Norwegian term for a sponge cake is “Sugar bread” (Sukkerbrød).
I think the problem is with bananas. A banana tree isn’t a tree; it’s an herb. A banana seat isn’t a seat; it’s a saddle. Sometimes the English language is just…bananas!
Language doesn’t have to, and often doesn’t, make sense. Like I said why is a cheesecake a cake and pumpkin pie a pie when they are essentially the same type of thing: a custard-type base flavored with either cream cheese or pumpkin, made by pouring it into a pastry crust in a flat pan and baking until the center doesn’t jiggle (or barely does) anymore. A cheesecake certainly looks and feels like a pie to me.
And whence sweetbreads?
There is sense and there is reason. The reason may not be logical.
I remain convinced that something usually served and created as a dessert is more likely to called a cake and that something originally created as a breakfast food (and then more savory) and still rarely served as the dessert to a dinner even in its current moister sweeter form, is more likely to called a bread.
For me, it’s as much the consistency of the final product. There’s general parameters, and most breads and cakes are going to fit my or your rule, but there will often be outliers because, well, language. Like where does “pound cake” fit into this? By my rule, that’s more a “bread.” By your rule, I think it would also be more a bread. But it’s called a “cake.” And I think someone mentioned “coffee cake.” What about crumb cake? I think of that more of as a breakfast food than a dessert, as well.
Hence why I used the qualifier “more likely”. 
Seriously though there are going to be several influences on categorization. Do the outliers, exceptions proof the rule?
Of the bread/cake products served at breakfast something has to as sugary as coffee cake to get past being called a bread.
I think of pound cake and crumb cake as desserts.
Here’s another test of the hypothesis: Mandelbrot (literally Mandel bread) and biscotti the cookie are nearly the exact same item. One is literally called a bread the other is a cookie. Mandelbrot is usually served with breakfast or brunch, occasionally in the afternoon, but not often as the dessert product with dinner and biscotti are not traditionally served with breakfast and traditionally are served after dinner with espresso or a dessert wine.
Well, isn’t that a borrowed word from another language, so their taxonomy may differ? At my coffeeshop, what everone else called biscotti, we called mandelbrot. It was eaten exactly the same. And poundcake I think of as a breakfast or brunch product, not an after-dinner dessert like other types of cake. If you tell kids they’re having cake for dessert and serve pound cake, most will be disappointed, I would think. (At least I would. But the dish is flexible.) If you look up “breakfast cakes” you’ll find both pound cake and coffee cake show up on lists, so it’s taxonomically ambiguous. I would definitely consider it more a sweetened quick bread than a cake, myself. For me, it’s mostly, can you butter it easily? It’s a bread.