Their hard work coupled with many others like them that worked with them made them rich. The same group of people could have been in another state and done just as well.
The people in California that made people successful are the Peter Thiels, Elon Musks and Keith Rabois of the area. VC money is the king maker. In the Bay Area it all started with Fairchild. It's the same reason why Seattle is successful. All the Microsoft money seeded the tech scene there.
These kingmakers have had enough of California and are leaving for greener pastures where they can continue to build successful companies without the state leaching off their work.
If they show up in Texas and other states and succeed in replicating their success, it will be clear it was them and not California that was responsible for the success. I'm glad California is rapidly losing its undeserved monopoly on tech.