Regular students on full scholarships can work any job they would like and earn as much money (from jobs, internships, fellowships, etc.) as they would like while on scholarship. Athletes on full scholarship are extremely limited in what they can do work wise (thanks to so many schools hooking athletes up with no-show jobs from boosters). When an athlete's uniform or name or image is used to make money for the school, conference, TV network, bowl game, shoe manufacturer, and so on, the athlete sees none of the revenue from that.
Texas A&M has an entire line of
Johnny Manziel gear on its website. But I'm sure they just picked #2 out of a hat and I'm sure the play on his last name on the Heisman shirt was pure coincidence... The only people making money off Manziel's image and likeness are Texas A&M, Adidas, and whoever the third-party is that runs the official online store. In any other walk of life, it would be illegal to not give Manziel a piece of the money earned from his image and likeness.
Without proper minor leagues in pro football or basketball, athletes are forced to play in the NCAA and it is not right that they cannot earn money off of their image and likeness when everybody else does.
Beyond making money off their image and likeness, the NCAA goes way too far restricting money they can make outside of an athlete's activities as a student. Look up the Jeremy Bloom case and the absurd ruling the NCAA made to ban him for life. Student-athletes have absurd restrictions put on them that other students don't have.
Like I said earlier, the best comparison is between an athlete on a full-ride and a student on an academic full-ride. Why is it that an academic does have the restrictive rules??? Oh yeah, because the academic can't potentially make the school, conference, bowl game, NCAA, shoe company, etc. a lot of money while a student, so there's no reason to whore them out while limiting them from making a cent outside of the scholarship.