I think it’s interseting that the OP did NOT ask for a dicsussion of driver location in cars, but rather for examples of totally unrelated things in our technology that are the way they are just because that’s the way they’ve always been. So far that’s certainly not the discussion he’s gotten back.
So, in the spirit of the OP:
Almost all technological conventions involved tradeoffs that were made (consciously or unconsciously) at the time. As the technology matures and becomes widespread, often the underlying tradeoffs change, making the initial choice less than ideal in light of later developments.These changes can be the result of improvements in different aspects of the underlying technology, or simply drift in the use of the product itself.
As an example of the former, the bandwidth used for broadcast TV is probably 20 times greater than if it was designed from scratch with today’s technology. Broadcast radio is similarly wasteful. But they did the best they could at the time with the tools at hand and now we’re stuck (until we replace it). HDTV is an attempt to do just that: smarter broadcast TV to recover a lot of that badly wasted bandwidth.
As examples of the latter consider that the CD was designed to store music, not data files, and has a lot of shortcomings as a data storage medium. The fact the internet is, at bottom, totally unmanaged & unsecured is a major design oversight for its current purpose, but made a lot of sense at the time it was set up that way.
Now on to conventions.
Why 110 (or is it 117) volts in the USA? Why not 87 or 175 or …? Why 60Hz? Why do electrical plugs look like they do? There are dozens of plug standards the world over, and damn few of them are really engineering-superior to any other. There are also thousands of other potential plug designs that aren’t being used. Why not? Decisions like this are inherently arbitrary at a certain level.
Why is booze 80 or 87 proof? Why not 65 or 94? Why are serving sizes for packaged beverages in the USA 12 fl oz? Why are fl oz the volume they are? Why not 20% larger or smaller?
Why drive on the right (in most places)? Why do traffic lights have 3 colors, not 4. Why red for stop? Why green for go?
Why are intersections with left turn pockets with green arrow lights almost universally programmed so the turning traffic goes before the straght through traffic? (In Tucson AZ they do it the other way, with left turners going at the end of the straight-through cycle. Seems to work slightly better except for the confusion factor for non-local drivers).
Why yellow stripes to separate lanes with opposite direction traffic and white for same-direction traffic?
Why are light bulbs sold by wattage (ie the energy the consume) versus by lumens (ie the light they put out)? Why are eggs sold by the dozen, apples by the pound, and (at least around here), grapefruit sold by the each?
Why do TVs have the number of scan lines they do? How come VGA connectors are the shape they are?
Why is the caliber of the M-16 rifle .223?.
Why does US lumber come in a size 2x4? Why is it really 1-3/4 x 3-3/4?
Why do we use a \ to separate the names of file folders (AKA directories) in MS products, a : in Apple products, a / in *nix & the internet, and a . in IBM mainframes?
etc. In any and every area of manmade products.
My (maybe a bit heavy-handed) point is that there are essentially arbitrary decisions made throughout the engineering process. Even carefully worked-out optimizations often end up with 3 or 4 equally good choices, so some folks in some meeting room someplace eventually say “OK, choice B it is. Go build it.”
One deployed, the installed base makes change difficult. The older the standard, the more likely that it’s become inappropiate for its current use. We know that railroad track spacing at 4’ 8-1/2" didn’t really come from Roman chariots (Snopes), but we do know it’s been that way for 150 years or so. We also know that for modern loads it’d be better to have a wider guage. IIRC, the Soviets standardized on 2 meters in the early 20th century because they didn’t have an installed user base to contend with.