It goes beyond that Big C. You can use Duck Duck Go and find articles relating to high school athletes. (in particular) who are leaving football for any number of reasons beyond grades.
As I'm sure you know, the incidence of concussions is one of great concern to many players and parents. Because football is now teaching tackling and blocking skills that incorporate leading with the helmet, proper skills are less prevalent. Manufactures keep trying to "improve the helmet" instead of coaches trying to improve the technique. So, understandably, many parents (and kids) are less enthused about exposing their kid (or selves) to increased possibility of serious injury through the game of football.
There is also a pretty hefty amount of money involved with football for equipment, and added insurance. It becomes increasingly challenging for middle and lower income families to promote football.
Additionally, for those who want to play multiple sports, it seems to be a sad trend that high school coaches are asking their players to commit to the game year round rather than getting the experience of participating in multiple sports.
And finally, (and this is one I think is ultra-important), the atmosphere around football has become one of self centered antics. Players dance, "talk", and taunt on a routine basis. A player will make a tackle, get up, and gesture to the crowd, or point to themself, or dance etc. just for making a routine play. The idea of sportsmanship is becoming increasingly rare in the game.
So for many of these kids, they are finding alternatives or just leaving the game altogether.
For those kids who particularly enjoy contact sports, there is rugby, La Crosse, and wrestling, all of which have cultures that promote sportsmanship and respect that are being lost in football. For those who don't have the same drive for contact sports, they can concentrate on other sports where their chances of injury are less.
So while your point about grades may has merit, it is far from the only reason for the decline of football participation. It is worth considering that the issue of grades has been around for many years. But the other issues have accelerated in recent years.. The game of football as you and I have known it, is not at all what it was in our youth, unfortunately.
It is a shame more schools don't offer wrestling (particularly in college). But rugby is experiencing rapid and noticeable growth. And I suspect that trend willl continue as people become less enthused with the college football game due to pay for play, NIL, portal, and re-alignments, all of which have taken some luster off the game many of us used to love.