Because these forks are seen by developers as an simple way to create massive profits for themselves. It's as easy as copying Bitcoin's source code, doing some adjustments, announcing it as 'the' solution to all problems Bitcoin faces, pre-mining, releasing, selling the pre-mined coins. It's becoming a trend, like the ICO hype. But I don't mind it, because I hold Bitcoins and these forks also make me richer.