Not everyone runs everything purely for the tangible rewards. I know a couple of people who play casually and don’t log on much, who run it as their version of a solo dungeon. I’ve told them they’d be better off in other content to get better rewards, but they enjoy DA. I’ve spoken to others who see it as something to do that’s not a cake walk; some like to sell the fragments; some even just think that it’s fun.
There are many players out there who choose not to follow the optimal path. You don’t have to play much to earn the entrance cost, (though that’s not so true for non-patrons,) and sometimes it’s nice to be able to do something like DA.