I don't mean this as a slight but because you/ they actually enjoy the game and the competition? Full disclosure my son decided to focus on academics ( Chem/Bio double major) instead of walking on at his preferred school due to his size. In the same vein as your son he felt the extra time devoted to football would be at the expense of his grades somewhat.
That's part of the problem with the decreasing participation is too many schools, coaches, and districts are forgetting this was, is and should be fun and enjoyable for youths. When kids are practicing and training for 12 months on a single thing quite often it becomes a job and not an enjoyable diversion. If a kid is really committed and wants to push themselves to be the absolute best they can be in a particular sport good on them but many are pushed by parents because its a means to an end (free college, NFL prospects of $, living vicariously etc...).
@Leeleesteeth When I was coaching and on a Pop warner board we had stats on sports injuries and soccer was far and away the leader in concussions, facial contusions and "career ending injuries" like Achilles, hip and knee blowouts. You had a very hard time convincing BMW soccer mom that football was safer for little johnny than soccer or lacrosse. both of which were growing in popularity in our area. Hell we went so far as to get an insurance breakdown "per child participant" and the female cheerleader was more than twice as expensive vs football player due to higher rate of serious injuries. We were prevented from dropping cheerleading by municipal "title IX" even though it was much more dangerous.