It is not about an oasis, it is about top of the funnel. To hire 1 eng, you have to interview 5-10, and have to phone screen 20-30, and have have hacker rank tested 100-200. Now scale that to a 1000 person eng team
Thing is that top of the funnel is not composed of majority local people. Many are people who relocated and many are people who are not local now but if hired the company would move them. If they can move them to SF they can also move them to another major tech oriented city.
That may be true but plenty of companies around the world that are nowhere near California somehow manage to hire technical talent. The Bay area has a higher density than many places but there's more competition for hiring too.
