I guess that's true for some suburbs. Maybe ones that are even closer to the city. Or in certain regions. In my area there seems to be an openness to multiple uses, lenient zoning, and variances.

I agree with the inertia part. I think some of it is 'build it and they will come' situation. But not about housing. Rather I think a lot of it is about infrastructure like public transportation and even better distribution of jobs. Also communities that share common values (tends to spur civic engagement and neighborly attitudes).

Maybe I'm just cynical, but I think we've largely become disconnected from out neighbors and even us-vs-them in our communities in general. If my neighbor wanted to put in a garage apartment or in-law suite type thing, then I'd be fine with it. So even if the zoning doesn't permit it directly, if I were to support my neighbor in a variance request, they would likely succeed. Similarly, if I were thinking about something that might impact my neighbors, then I try to get some input from them. Make sure that if they have some concerns I can try to address them. Maybe I'm just weird or have great neighbors, but it seems many people just want to sic the government on their neighbor at the first opportunity.