See: www.latimes.com/sports/highsch...20150925-column.html
It's even worse at the youth football levels. I have a friend who has been very involved the past dozen or so years as a coach and administrator in a youth football program (Junior All-American) around here. He says that a decade ago they fielded full teams (30 - 33 players) in all six age/weight divisions (Gremlins, Midget, Pee Wee, etc.). So roughly 200 kids in the program. This year they can only field four teams, and most of those are not full (e.g., the team he is coaching has 21 players). So overall numbers have been cut in half. And a decade ago there were 32 teams in their conference, all with similarly full rosters. This year in his age/weight division, there are only 21 teams, most without full rosters. Again, overall numbers of participants have been cut roughly in half.
I know this isn't a football site, but I think the implications of these trends -- if in fact this is or becomes a nationwide trend -- are interesting for high school sports overall.