You didn't control for corruption.

Surly the “corruption” is big corporations pushing for the H1B program in the first place, at a time (early 1990s) when decreasing immigration was overwhelmingly more popular than increasing it: https://news.gallup.com/poll/1660/immigration.aspx. Surely the “corruption” is the government looking the other way for years while Indian body shops imported massive numbers of foreign workers while ignoring the requirement in the law to advertise to americans?

And this is hardly new. Ross Perot was opposing H1B when he was running for President in the 1990s.