They're getting the chance to showcase their talent for NFL teams and potentially make millions of dollars. They're also getting a free degree and a chance to land a cushy job after graduation from the local alumni. If they feel they're being exploited, they can decline the scholarship offer and see how well things turn out without a free ride to a college and a chance to build their resume' for an NFL career.
Texas A&M raised $740M this past year, which was more than the previous four years combined. They've probably sold hundreds of thousands "#2" jerseys in the past year. I don't like Manziel at all, but to say that Texas A&M didn't make an absolute killing by having this kid around for a year would be straight lying.
He could shatter his leg this weekend and all he'd walk away with is an average degree and a shiny bronze trophy. Meanwhile Texas A&M gets $200M to renovate their stadium with and gets to use his name and likeness until the end of time.
It's a pretty ****** deal for big time players. It's why the NCAA is terrified of the Ed O'Bannon lawsuit and why the straight up dropped video game licensing.