Check this out.
In football, an enrolled student-athlete (as opposed to a prospective student-athlete) may enter the National Football League draft one time during his collegiate career without jeopardizing eligibility in that sport, provided the student-athlete is not drafted by any team in that league and the student-athlete declares his intention to resume intercollegiate participation within 72 hours following the National Football League draft declaration date. The student-athlete’s declaration of intent shall be in writing to the institution’s director of athletics.
This rule has been in place since 2002, and it’s unclear why nobody is taking advantage of it. My guess is the athletes don’t know about it.
Somebody should tell them.