> We see this with all those "mixed use" buildings going up in Silicon Valley, with retail spaces on the ground floor. It's really hard to fill those retail spaces.

Yeah, I think this is because (1) Silicon Valley's housing shortage far exceeds any retail shortage; (2) such retail is often added just to encourage NIMBY city councils skeptical of new housing to acquiesce as part of a "community benefits" package, not because there's any actual market demand for retail; (3) in places like San Francisco, there are so many bureaucratic roadblocks in the way of retail such as the formula retail restrictions, discretionary review, and hostile neighborhood organizations like Calle 24 that act as gatekeepers to opening, that a lot of potential small business owners just won't bother. In a healthy market, I suspect you'd see these spaces get used more.

The problem is that all of those places are planned. I get major 'Soviet Central Planning' vibes from the USA when it comes to zoning and planning out cities. Of course the people making the decisions on planning have no idea what will work. They only know what will work in the most rudimentary, scaled up, sense. Small shops need to be allowed everywhere, rules about minimum parking, lot sizes, use, etc need to be relaxed to allow those things to even be possible.

Suburbs are literally rooted in racism.

That sounds hyperbolic, but the first suburb in post-war US was a planned whites-only community to escape the city. (Levittown)

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With that said, yes, the US purposefully planned blocks of cities to be dedicated to one purpose. This promotes car culture which, surprise surprise, car and oil companies were big into lobbying to shut down mixed use and public transit, and continue to be.

Mixed use areas are typically either big cities, have pre-war origins where it has basically always been mixed use or typically both.

The mixed use buildings you're referring to are approaching from the wrong direction. They're 1960s style office parks - sometimes a modern reinvention of them, sometimes literally a redevelopment on the same land - and you can't get a meaningful mixed use space in an area where everyone drives in at 9 and drives out at 5.

Cities virtually everywhere in East Asia have convenience stores on almost every corner. They manage pretty well.

Well of course, who can afford the rent? It's not like a little four-employee computer repair shop can show up and fill the space.

Even if the rent was subsidized or more likely rent-controlled -- you still have to pay those four employees enough to live in commute range. That forces the margins you have to charge for computer repairs to shot up to a level that would make the Geek Squad blush.