I concede that a student athlete can obtain funds from other sources. So, their argument that they are broke is not entirely legitimate.
At the same time, nobody in this thread has answered the underlying question: Are athletic services "employment?" Along the same lines, how are student A (compensated graduate assistant) and student B (uncompensated student athlete) any different? fundamentally, why are they treated any differently? both are students, both are getting benefits, but one student is paid by the university for their services whereas the other student is told to eff off.