In my opinion, they didn't release them because:
1) they thought they were "smart" and wanted to capture new fans with "updated" beats. Turned out to be a fukking terrible idea
2) Contract disputes and/or samples
3) Afeni (I ain't gonna say why, outta respect, but you know...)
4) Suge being in jail for too long
I think Afeni has a lot to do with it though. She wanted too much control. Yes, she is his mother, but, she kinda fukked up with releasing shyt. Giving Afeni half of the rights, was the right thing to do, but was bad for his music...