It’s possible that is exactly what’s happening. It’s also possible this wasn’t really the right place to ask, since it’s like asking a fish if the water is comfortable compared to other things.
I’m pretty sure there are both lumpers and splitters on both sides of the Atlantic. Are rabbits rodents? That’s gone back and forth a couple of times since i was a child, and I’m pretty sure a lot is the people driving the change (in both directions) are American.
On the one hand, i don’t think “shepherd’s pie” is a pie, because it has nothing in common with pie. As @pulykamell points out, it’s a pretty ordinary casserole, and would certainly be called “some-descriptive-word casserole” if it had recently been invented in my part of the world. (Hot dish is Midwestern, i think. I’ve never heard anything described that way “in the wild”.) On the other hand, it’s certainly called “shepherds pie”, and other than being surprised by the dish the first time i saw it, I’ve never been bothered by the name.
I’m sure there are lots of words that are used more generally in American English than they are in the UK, although I’m not sure what they are, because I’m not as exposed to people from the UK as you probably are to people from the US. Maybe “pants”? We have all kinds of pants, underpants, sweatpants, jeans, ski pants… I think that word is more narrowly defined on your side of the pond? That’s a word that wouldn’t surprise me if it popped up in some new and unexpected usage, because it’s already very general.
I don’t even think that’s meant to be cheeky. It’s got a crust on the bottom, like every other pie. Quiche is another common savory pie.
By “Shepherd’s Pudding”, I mean mutton, vegetables, and gravy in a pan, covered in mashed potatoes, and then baked. And by “pie tikka masala”, I mean a lower “crust” of a layer of basmati rice, topped with chicken or other meat in a spicy sauce.
Is that a pudding, and a pie? If not, is that any less “splitting” than an American saying that shepherd’s pie isn’t a pie?
I don’t really care what you call it. I don’t require you to make things to conform to my ideas of categories. That’s sort of my point.
Indeed. The question is whether the proportions of those things are the same on both sides.
Yeah, but I don’t consider anything with just a bottom crust a pie. Something like a Chicago deep dish would be more like a pie to me, but what other pies can you think of that only have a bottom crust? Quiche goes around the side. If you put a bunch of apple on a flat crust, I wouldn’t call that a pie. It’s some other kind of pastry. When I use the term for pizza, I always feel a little cheeky using it, but not as much as if I use “za”.
Most cream pies?
I’d classify shepherd’s pie with something like beef stew with dumplings. If I didn’t know the know the name, I’d never think “pie.” But as @puzzlegal said, Americans never automatically think “savory” when pie is mentioned.

Americans never automatically think “savory” when pie is mentioned.
Around here they do. And sometimes Shepherd’s Pie is made with a bottom crust, sometimes a top crust, and sometimes both.
You can’t generalize about all Americans in most cases, and certainly not when it comes to food genre.
Really? Huh. I guess I’ve never had a proper cream pie.
Who the hell puts a top crust on a shepherds pie? That’s a new one.

If you put a bunch of apple on a flat crust, I wouldn’t call that a pie. It’s some other kind of pastry.
I don’t think I’ve ever had a pizza with a completely flat crust except maybe frozen - the edge is always a little higher and doesn’t have any sauce or cheese on it. Kind of like a quiche.

Who the hell puts a top crust on a shepherds pie? That’s a new one.
It’s not a pastry crust - the mashed potato is functionally a crust. Never seen a bottom crust of any kind, though.
Beats me. I saw a recipe. French Canadian meat pies may or may not have a top crust. Mostly I see full size 9 or 10" pies without a top crust and little 3 or 4" pielets usually have a top crust. I
wouldn’t put a top crust on a Shepherd’s Pie. To me Shepherd’s Pie is all about browning the little peaks on the mashed potatoes.

Around here they do. And sometimes Shepherd’s Pie is made with a bottom crust, sometimes a top crust, and sometimes both.
You can’t generalize about all Americans in most cases, and certainly not when it comes to food genre.
I didn’t mean to be so doctrinaire about it, but I’d be surprised if it’s other than a vanishingly small population that would. Like pasties are common in Butte, but not in very many other places in the US.

I don’t think I’ve ever had a pizza with a completely flat crust
Come to Chicago.

It’s not a pastry crust
A pastry crust is what was implied in the response.

French Canadian meat pies may or may not have a top crust
Are you talking tortieres and the such? Yes, those are pies.

I didn’t mean to be so doctrinaire about it, but I’d be surprised if it’s other than a vanishingly small population that would. Like pasties are common in Butte, but not in very many other places in the US.
I’m pretty sure that is the case.
At least around here, pizza is round, and pizza crust goes up the sides a bit, and contains the toppings. Like the crust on quiche, or pumpkin pie, or lemon meringue pie.
Pot pies are unusual in that they are savory AND they often don’t have a bottom crust. But they have a top crust that is very pie-crust-like. I think of them as a type of pie.
Shepherds pie has nothing in common with other pies. It’s savory, it’s typically cooked in a rectangular pan, and there’s no pastry involved anywhere. At least, I’ve never seen one with a bottom crust, and the top is mashed potatoes. I guess if you spooned it into a pastry shell it would be a pie. But that’s true of every other casserole. It’s a pretty ordinary casserole.
Pumpkin pie, lemon meringue pie, key lime pie, pecan pie, chocolate cream pie, and cheesecake pie all seem to me to fall squarely into the range of what Americans typically call “pie”, and typically none of them has a top crust.
yeah, those are all “typical” pies in my mind.