>As I understand matters, it started in the 70s and 80s as states pulled back from funding public institutions.

Yes, absolutely this, and accelerating heavily in the late 00s after the financial crisis. In some states, especially for non-flagship universities, you can overlay the decrease in state funding and tuition increases and they're nearly the same line

Tuition explosion isn't all just the proliferation of assistant deans and VPs (although that is a problem, too), a huge portion of it is that public higher education is essentially public in name only these days