The fact that most folks in CA are from out of state doesn't imply that they would be just as happy in Texas. Something like 40% of our STEM workforce is from outside the country. Do you think an immigrant would be treated as well in Texas as in California? (maybe this is my prejudice showing, but everything I've seen and heard is that they would not.) add to that the developers who aren't heterosexual (or who are but who don't look it) or who aren't white, and I think you have a lot of people who... probably have good reason to stay on this side of the mason-dixon line.
(I feel the need to add a disclaimer; I've not spent a huge amount of time in Texas, and perhaps it isn't so bad, but... this perception is common, and it does mean some people won't take jobs in Texas, just like the perception that California is a nanny state where you will get fired for not being politically correct will keep many Texans out of California.)