The risks football players usually face involve only themselves.
Of course with COVID, there are other parties involved -- all of these players have parents, grandparents, classmates, trainers, etc.
So even if a football player says he's healthy and willing to take the risk, it's still probably a bad idea to let them do it.
If the experiments with MLB etc were 100% successful, I think one could make a "let's just play" argument. But given what we've seen, I think the balance tips in favor of not playing