There are lots of companies in the Midwest that will pay mid six figures for a non-manager SWE. I will concede that there are fewer such jobs in the Midwest.

I'm not convinced that jobs in the Midwest generally pay less than in California because of cost of living. It may well be that SWE openings in the Midwest are generally for less-skilled SWEs precisely because it's not worth paying California salaries for those roles.

This rings true to me because, well, there are companies in the Midwest that will pay mid six figures.