They are being paid for their name, image, and likeness by an organization in the United States which is earning income in the United States which is in violation of the rules on having a student visa.
If they didn't revoke the athlete's student visa, there would be federal lawsuits by every foreign student who was denied the opportunity to earn income or who was kicked out of the US for violation of that rule for having a student visa (as well as likely every upcoming opponent of that school). If they didn't report the income, then they didn't pay taxes on it, which is then tax evasion which is a felony, which also gets your visa revoked as well as possible imprisonment.
And would you really risk your visa getting revoked and being permanently denied entry into the United States?