Depends on the surburb, I've definitely seen many where walking distance wouldn't work very well, there just flat out aren't that many people. You'll have a subdevelopment where there's 50-100 houses or whatever, and it's connected to a highway and otherwise surrounded by a bunch of green space. That's not enough people to support more than a kiosk's worth of retail, probably.

I mean, that's really a self-reinforcing cycle. Car culture leads to car-centric development leads to car-dependent suburbs leads to more need for car infrastructure. Nothing said those suburbs had to be built that way, except that's what people expect (and whatever local zoning ordinances ear-marked the land for single-family homes).

Agreed. But nevertheless, those types of suburbs will be harder to convert to a more walkable or bike-friendly format.

But yes, many others would be fairly straightforward, the only blocking issue is political will. "A bakery on my street corner makes me scared for my neighborhood character" is a surprisingly common sentiment in the states. People don't want any kind of retail whatsoever.