So it's been a day or so since we first heard that Death and Taxes was disbanding, and since then, DnT member Xi- has posted a somewhat lengthy explanation as to why. In the end, the biggest reason Xi- gave is pride. Many people, he says, just stopped thinking about the raid and the guild as a whole, and were more focused on their own advancement and their own needs, and became impatient when a boss did not fall easily. When it was time to progress, many of them, even officers, would disappear and stop supporting them.
But the point about pride, about guild members who disappear for a while and expect to pick back up where they left off when they return, and about people who never show up for progress kills, or show up and complain if the boss doesn't fall after one or two tries, that rings true with me, as I am sure it rings true with a lot of current and former MMO raiders, whether from WoW or other games.