#1 reason is lack of patience. Crota doesn't die in five attempts and people start leaving. Then you have to replace them and integrate them into the flow. It's the first week of hard mode and you expect him to die in five attempts? Cmon people. Crota is still easy compared to other games with raids but it's the first fight that you have to give thought to your talents and gear set up. And the funny thing is that the once piece of gear that people are obsessed with, GHorn, is so not necessary. Then when you throw in the disappearing sword bug, the Crota kneels for one second bug and the random attempt where the Sword Bearer runs and hides it's no wonder people aren't killing him.