I worked for a couple of very "household name" big companies as a tech lead. I trained probably dozens of H1Bs over the past 15 or so years. I've seen it all. I decided that I would help anyone who wanted to improve their skills regardless of their origin or employment status, and that's what I did. I got mistreated terrible at times, in particular by a Venezuelan woman, but generally speaking, I helped raise the bar for a lot of people who maybe otherwise would have been ignored because big companies don't care about training people at all. As I look back on what my career was, I think that all the informal mentoring I did was probably my biggest contribution. I just wish it had turned out better for everyone involved. I saw a lot of absolutely heartbreaking situations arise over the years. And now my situation is kind of heartbreaking as well. We were all in this together, but nobody spent a single second thinking about that.

as an American who worked in Silicon Valley for years, but is not from there, i'd say it's also "captive real estate customers" created by H1-B people.