There are multiple factors at play here:

There are 4 million fewer college students than there were a decade ago. Among students who graduated high school in 2016, 70% began college that fall. In 2020, that number dropped to 63%.

Source: Fewer People Are Continuing Their Education After High School | Watch

The numbers I find are closer to a 3 million loss, rather than 4 million but the variation can be due to what is counted as a college student – some are in the age range 18-24 – while others may be all ages, or only 4 year colleges, and so on.

College Enrollment Statistics in the U.S. | BestColleges

Why the drop?

One, of course, is the drop in the number of young people due to the past decline in fertility rates. The linked item, above, goes into other possible reasons for the decline.

In this chart, below, look at age 30, then look at age 20, then look at age 10. It’s a double or triple whammy of reasons from fewer students, to high tuition and fees and more.

Coldstreams