In my experience, sports becomes a way into college. Academic scholarships are few and far between, especially at state colleges. And it seems, a lot of families haven't really saved any money for the kids college fund. So for many families here, it seems sports scholarship, or community college. The high school doesn't help with that story. You should see the signing day news spreads my district puts out. Care to guess how many news items are about the academic scholarships, or the few in a very large district that get a full ride because of their academic accomplishments? That would be zero.
And you know what the kid has to do to qualify to play in that sport/activity? In a lot of sports, if you didn't start by the time you were in kindergarten, you missed the window. If it is something that just recently became popular, or they don't start until later, like lacrosse or volleyball, then you are paying thousands of dollars in off season to get your kid more experience, training,whatever. It is a small investment, though on the parents part, since the parent seems to know that their kid will get the full ride scholarship for college. Do they think the kid will do it professionally? Probably not. Do they think it will get their kid into a good school, and allow all parties to be debt free at the end of it? Yes.