There are not anywhere near enough American-born skilled software engineers to supply the US tech industry. Take foreign-born software engineers out of the picture and the majority of software engineers in Silicon Valley are gone.

You can't make up for that by just offering higher wages. Maybe a few top companies would be able to manage it, but only by poaching all the engineers from other companies. Ultimately, the industry will move elsewhere if US companies can't hire foreign engineers. The US only supplies a fraction of the world's software engineers. There's no inherent reason why the world's tech sector has to be so concentrated in the US.