A rational answer to the psychological question would be: they despise the people who are destroying the object of pleasure that was given to them in 2006. Are those the very same people who gave DDO to them? I don't know, some might be, some might not.
How are they destroying the game? Its been discussed too many times lately. To make it short: unpopular changes or lack of popular changes.
Whats the purpose of all these angry threads? To make Turbine interact better - and listen to - their players.