There's a little more to it than that. They have to make progress in their core classes. They can't just pad their schedule with 100 level classes.
Last summer a UMich academic counselor was on the radio talking about how she helps kids. She said it can be difficult for athletes to change majors because of the required progress with core requirements. Say you start as an civil engineer and you have the required core going into your junior year, it might be possible to change to EE or ChemE. Switching to journalism would be almost impossible and stay academically eligible. The engineering core doesn't overlap the j-school core enough to be able to meet the required core hours.
So break the law, break school or team rules, or go against social norms and you can overcome your mistakes and play. Choose the wrong major and you're stuck. Just another instance of where the NCAA rules suck.