There’s always a reason that stuff wasn’t released in the first place.
Yes, but not necessarily an artistic reason.
This may have been legal problems reason................
In Prince’s case it’s often just that he was a moody guy and by the time he finished a product he often had lost interest. One of the problems of being a touring musician is that you carry your songs with you. You release an album then go on tour you’re expected to play some stuff from that album, and if it’s stuff you really really liked playing ONCE that can be a burden. And with as much stuff as this guy produced, he really just seemed to have a need.