A basic look at the economics will show how stupid it is. They get room and board in a usually mid-major city paid for them. That's like $1500/month. They get an education, that's like $20k/year.
So let's do some quick math:
Now on the other hand if universities had to pay athletes they'd probably cease doing all that. So let's think about how much the average college athlete is worth.
The AFL minimum salary is $31,000 but the median is like $45,000. Keep in mind that many of the AFL's players are former college standouts. The average college football player isn't a standout though, you're more likely to be a bench warmer than a standout.
So the average CFB player is worth signifigantly less than $45,000/year. Even being generous and saying they're worth $25,000/year on average, they're still significantly worse off than they were before.
Now let's focus on college basketball:
The NBA D-league pays it's players a max of $25,000/year but an average of $19,000/year. Housing is provided for them though so let's say they get a total of about $37,000 per year.
Just like the AFL, the D-league is filled with college standouts. Just like college football college basketball has far more bench warmers than standouts.
So let's be generous again and say the average CBB player is worth $19,000, once again they're worse off.