Musicians, actors, etc. are not in competitive events. Fans want some form of actual competitiveness in sports. The NFL is hugely popular largely because it built in ongoing competition/parity enhancing rules like draft order, salary cap, etc. The NCAA, while not doing as good a job as the NFL, has also built in competition enhancing rules like the different divisions D1s-2-3, quasi-amateurism at D1 and D2, scholarship limits, D3 scholarship bans, etc. NCAA D1 football is hugely popular largely because of the structure set by the NCAA.
It's not about the free market. The NCAA participates in the free market. Participating as an athlete in NCAA football under its rules is 100% voluntary. The NCAA, with its amateurism rules, has kicked ass on every other football playing organization for young men aged 18-22. The NAIA tries but is losing ground (with similar but more loose amateurism rules). No one is stopping other pro, semi-pro and development leagues from forming and competing for the same players - but time has shown it's more about the individual school's brand and the NCAA structure, than it is about individual athletes.
It's not about justice. For the uber talented athletes, NCAA football is a celebrity-level low paying internship (free ride scholarships) that could result in tens of millions of future dollars if successful. For mid-level scholarship players, its notoriety that couldn't be found anywhere else plus a free ride, etc.. For walk-ons, its everything else student athletes love about athletics.
In the end, if the legislation passes in wacky CA and it spreads elsewhere, I could see the NCAA creating a fourth (really 5th?) football division for schools that allow outside endorsement money. I can't see any of the Big Ten schools willing to go down that road with the possible exceptions of Ohio State and maybe Nebraska. As big as Michigan's athletics are, it's a high academic school and I don't think they'd go there. Amateurism is not dead. It's healthy has hell in D3.