Cuz Akon doesn't give a shit what 50 Cent thinks of him collabing with someone else.
50 getting mad at Akon isn't gonna get 50 anywhere..but down a path where it's a huge loss to himself. Akon's like Nate Dogg, everyone loves him...so if he can get a single with Akon on it, more than not, it'll probably be a hit.
Jada, Fat Joe...etc, not so much.