End game... Bored. The facts.

[Conkers]

snip

Lots of MMOs are "successful" initially, however 2 years down the line things are very different with rare exceptions like WoW, EVE Online, etc, just to remind you the fastest selling MMO before GW2 was SWTOR...

GW2 does indeed release content every 2 weeks, the problem is it is usually fluff content and rather mindless (with the odd rare exception), it also comes at the expense of other areas, hence people that wanted challenging PvE with meaningful teamwork left in droves, sPvP is virtually dead, guilds with thousands of members looking for DAoC 2.0 left in droves, because WvW was not up to it, nor recieved the attention needed to improve it, etc, so what is left of the GW2 playerbase is largely kids, and players who are fine with mindless content.

Also there has not really been a new triple AAA MMO released since GW2's launch, so you have a lot people that are now just using it as a stop gap until Wildstar & TESO come out.