H1B's already need to exceed the prevailing wage, as determined by DoL.

You can argue about where they actually end up, but it's not the bottom 20%. Esp once you figure in immigration related overheads (that's staff, not just fees and travel).

Higher salaries for H1B's would require the right to change jobs easily, unlike now where there's a tremendous risk. And then there's L1's, who have no negotiation power at all.