Since we are using Northwestern as an example, these students are receiving nearly $63,000 in free benefits for being a college athlete, not counting coaching. So I'm not sympathetic to the idea that these athletes are "employees" even if they are being handsomely compensated for their athletic ability.
As the story notes, the players are backed by the United Steelworkers union. Unions these days are, instead of trying to do right by their members, trying to expand their waning influence as more and more people are forgoing union membership. When people have the freedom to work in their field without joining a union, as those who live in right-to-work states do, people often choose not to join a union because unions tend to benefit union leadership more than the union rank and file.