I think it's really as simple as having a big company hitting a giant IPO that creates wealthy individuals who go on to invest in smaller up and coming startups. E.g. Seattle has Amazon and Microsoft, Bay Area has Meta, Google, etc.
This is what happened in Waterloo, Ontario with Blackberry. Of course the tech scene there is no where near as large as a SV and a couple others, but it's still weirdly big and concentrated given the size of the surrounding city. Every mid to large tech company in that area has a decent size cohort of ex-blackberry people.
Is it possible that the cause and effect are reversed? I thought RIM was established in Waterloo because Waterloo was already by that time a Silicon-Valley-like (or at least Pittsburgh-like) tech hub.
That could definitely be partly the case! After reconsidering it's definitely not fair to attribute the regions success entirely to RIM. It also probably has a lot to do with the University of Waterloo, which (being much more recently founded than other Canadian universities) has always had more forward thinking STEM programs and faculty, and also has much better IP protection for students than other schools in the area.
If that were even remotely true then Silicon Valley would already be in Bentonville, Arkansas.
There are a ton of programmers in Bentonville, AR. I know some of them. The needs of Walmart are narrow, so it's not going to be the skunkworks-lousy valley, but for what Walmart does, it creates a community of IT contractors.
That's not what pyrito said, though. Pyrito claimed that the necessary and sufficient condition is a critical mass of rich people, a fairly doctrinaire application of "trickle down" economic theory. But we can see quite clearly that the Waltons, despite being fairly numerous, close in geographic proximity, and unbelievably rich, haven't triggered a Silicon Valley-like phenomenon.
I would be surprised to learn the Waltons actually live and spend much of their time in Arkansas.