The originating concept of sports in the 19th century was club teams. Meaning you had to be a member of a club, an organization (like a workplace) or a college to be eligible to play for that team. Of course, human nature being what it is these club teams immediately started bringing in "ringers" specifically to try to win (thus circumventing the spirit of the eligibility rules).

In North America, sports such as Baseball & Hockey just dropped the idea of club teams & went to the more honest professional route where the best players went to whoever paid them the most. Football, however, stayed with the club model with colleges being the highest level (its hard to comprehend but it wasn't until TV & the late 1950s that the NFL was even a big deal... and that was because of the NCAA f'n themselves in regards to TV until the 1980s). Basketball, which was basically invented as a college sport followed Football's path.

College sports boosters have always tried to cheat to give their teams an advantage & all the rules we are talking about were put in place as a reaction to the shit boosters pulled. Why are players not allowed to have outside jobs? Southwest Conference (Texas, SMU, Oklahoma, etc ..) cheating in the 1970s where athletes were promised "jobs" and salaries by team boosters that they didn't have to show up to.

Why were there rules against what Nike/Adidas did? Because if you take money from Nike, you damn well better go to a Nike school (Ex: Oregon/Clemson/Alabama/Duke/North Carolina) vs Adidas (Ex: Kansas/Louisville/Miami/Nebraska) or Under Armour (Ex: Notre Dame/Wisconsin/UCLA).

It all comes down to the same concept... The NCAA rules were not actually about preventing athletes from making money, they were about keeping the colleges (and their supporters) honest in order to try to maintain a level playing field. Massive TV and merchandising deals by the colleges which translated into an arms race in relation to sports facilities & coaches have completely undercut all of that & made the entire ruleset for college athletes not getting paid based in the dollars they generate hypocritical.

The question becomes whether you throw open the doors and make it the wild west (Professional leagues in North America are so against this that they prevent it by drafting the rights to players) or you set up rules to govern it... And if you go the rules route, what are they & who represents the players interests in those negotiations?

Saying "pay them" is as simplistic as saying "drugs should be legal" or "the police shouldn't shoot people"... But it gets extremely complicated when you get into details of what those simplistic statements mean.