Well it's a silly question. It's like asking a fan of a sports team "Why are you still a fan?" when someone complains about how bad the team is. To answer the silly question, it's because people enjoy a lot of aspects of the game and see how much potential it has, and most people hope that Bungie will one day actually put in the effort to let it reach that potential. We see glimpses of it here and there, but 90% of the time it's just filler/chore like content that is forgettable and boring. It's tough to love a game where the developers don't care to make it as good as it can be, and constantly lie/ruin the experience by adding/taking away stuff that nobody asked for.