You have to understand that nearly all cities were shitholes in 1989 until the Urban Revitalization of the late 90s. This wasn't an SF specific thing. NYC, for example, had over 1200 murders in 1992 (!!!) compared to last year's 414.

SF's revitalization has more to do with that than with "tech" jobs. I know in the Hacker News echo-chamber its hard to think there's anything but Internet Tech in SF but it's got ALOT more business than that -- It's the largest banking center on the west coast, got a massive bio-tech footprint, has some major apparel companies (Levi and Gap and a bunch of smaller ones), etc, etc. It's pretty diversified.

What caused the "urban revitalization"? Was it just that people who hadn't been around during the 1968-~1980 urban hell were finally in a position to be buying their first homes?

Honestly, I don't know so I'm going to speculate based on experiences. I think it's a generational thing. The younger generations seem to want density, to be around things, to not own a car. I think growing up in large suburban homes, there's been a genuine desire by younger people to move to cities and away from that lifestyle.

You can see this happen in many ways aside from city's becoming safer: Real estate cost increases in cities, The whole bike-movement is an element of it, NYU getting 44k applications, the growth of the Brooklyn "brand".

I think, generally, there's a real desire for an urban community with culture and shared experiences. I know I don't have anything more 'concrete' to back this up, but this is the general sentiment of my friends (in their late 20s to early 30s.)