I've raided in both WoW and LotRO, and what I've seen as a semi hardcore raider at the time is if not enough end game content is delivered, raiders leave. You can do the same raids only so many times before you are bored to tears.
Are they becoming an outdated part of MMOs? Maybe, maybe not. Not enough new open world content, players leave. Not enough new pvp maps, players leave. It's vicious cycle. Also having a company string out what they have for months/years at a time (looking at you Blizzard) players leave.
As the available pool to recruit/pug from dwindles, it gives an impression of no one wanting to do them, but in the end you can really only blame the developers for driving away customers. I dont think IMO is has anything to do with players being anti-social or wanting epics NOW without working for them (although there are some out there that would love this) it's just that most have done current end game content ad nauseam. This leaves players like myself who have come from other games out in the cold trying to see what is new for us.
I think I've strayed off the topic enough, so I'll step out now.