https://educationdata.org/college-enrollment-statistics

>62.8% of high school (or equivalent) graduates go on to postsecondary study.

>Enrollment among new high school graduates has declined 10.4% since its peak in 2009 (70.1%).

There are still a lot of kids that could go to those 3rd tier universities, but choose not to. The cost/benefit is not perceived to be there anymore.