Years ago, a survey asked students who didn’t take any summer courses after expressing interest why they changed their mind. Some had work conflicts, one had a technical problem logging in (and therefore gave up, apparently), et cetera.
My favorite explanation is this one, repeated here in its entirety:
I got into college
Yeah. You wouldn’t want those college courses to get in the way of your college courses.
It’s a little known fact that people who get into college do not need to take college courses. I personally am one of those people. Contrary to what the Dean said in his expulsion letter, the reason I did not do the classwork was because of the coursework. And vis-a-versa.