Total unprofessionalism and what seems to be nothing but dogshit friends/family/business associates around him tend to do that. Not a smart guy to begin with, so hard to overcome all that dead weight pulling him down.
I saw a highlight of a fast break dunk the other day and nothing that made him exciting in his first few seasons was on display.
Also, when the ABA started allowing dunks again in 1973 the league counted them separately on the box scores. League leader in 1973? Larry Dunque.