The apartment (flats) issue is one that has some exceptions, in the USA, as I've seen single family homes and small duplexes, along with larger complexes that have inaccessible units - I think over a certain size, at least some percentage have to be accessible (just as a bathroom has to have at least one accessible stall, but is not required to have more).
Residences and rental units are not required to be ADA compliant. A multi-tenant residential building must be ADA compliant in the common and public areas of the building.
For residential rental units, landlords must make ‘reasonable accommodations, unless they would impose undue financial or administrative burden,’ which means if you get paralyzed while renting an apartment that isn’t ADA compliant you’re probably fucked unless you can afford to add a ramp yourself, and pay to have it removed when you leave. Adding a wheelchair ramp would be an undue financial burden, so a landlord isn’t required to add one. Replacing the door to a unit with a 36” wide door would likely not be considered an undue financial burden, so if you live in a building with ADA compliant public spaces and elevators, you’re probably OK since the landlord will likely install a larger door.
Government owned housing is required to be ADA compliant.
Europe is diverse. The parts of Germany I happen to know, are mostly ADA compliant, or even more so. From the little bits I know about stuff like that. Anything wheelchair accesible I tend to notice as avid bicyclist. Other things are clearly visible, audible, or tactile. Like textured markings on the ground for the blind, braille markings on all sorts of buttons, near screens, acoustic signaling at street crossings, in stations, doors of buses & trains, lifts, in all sorts of public spaces. If there is something wrong with that, say a lift for acessability of platforms, it's in the local news. Which doesn't necessarily means it gets fixed fast, depending on who manages that property. Let's say Deutsche Bahn, which is mostly foobared.
Anyways, that is NOT the case in the parts I know of the US. Much less markings, much less signaling, much shrug, so what?
I guess the US are diverse too, uh?
What comes to mind for .de and its ADA-equivalents are:
Beeping or 'knocking' drifting slowly apart, to randomly come to be synchronized for a moment, then drifting apart again. I think I'd go crazy when I'd have to live near such things.
Otherwise, during daily life I tend to be annoyed by all that beeping.
Yes, of course Europe doesn't have any US laws but to suggest that it doesn't have legislation about accessibility is simply wrong. Guess what... the legislation generally applies to buildings and construction post-dating the legislation. Applicability to earlier structures will vary depending on feasability and justification (cost, traffic).
US businesses are basically all wheelchair accessible - easily, too. Most sidewalks have curb cuts at street crossings. Ramps are commonplace.
This is NOT the cause in Europe, and not only in the historic old buildings.
Even using a stroller is noticeably different; I can’t imagine being in a wheelchair in some cities.