For public (state-funded) universities, they receive a large percentage of their operating budget not from tuition or endowments, but directly from the state. I

For public (state-funded) universities, they receive a large percentage of their operating budget not from tuition or endowments, but directly from the state. In many cases, over the past 10+ years, this direct support has been slashed. So, for these institutions, even as tuition has been increasing, their total budget was likely dropping. Tuition hasn't been able to keep up with the loss of state funding, so the universities try to make the numbers work in a variety of ways... one of which is to limit the number of professors.