After many raids with people on these forums I ask myself this very question.
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The vast majority of this player base does not understand the mechanics of the fight. They don't understand really what's going on around them. Every role needs to be done consistently and without death. This general lack of understanding the roles (especially other's than themselves) leads to wipes. They don't focus. They expect a carry to a degree. "as long as I contribute dps..." doesn't work here. If you've been here long enough you saw the madness when bungie switched who Atheon teleported.