This is probably related to teenagers enrolling in college not only for an education but also for the amenities that come with college life (think of greek life, moving away from parents, college sports, freedom to explore your identity, etc.) The pandemic has put a stop on most of all non-academic stuff, making enrolling in college less appealing to this group of students.

It will be interesting to see a follow-up analysis that parses out enrollment behavior by subgroup (e.g., by SAT/ACT score) as it will be easier to understand who is choosing not to enroll in college.

Another follow-up could be to see which institutions are losing students. It is known that college enrollment is counter-cyclical to the economy and that enrollment declines at community colleges and open access universities when people can get a job right out of high school.