People getting jobs to max level in a few days because of Abyssa... This along with seeing 14 coming out, showing just how dated the game had become, and knowing that sooner or later that perfect gear set you worked for years on will mean nothing sealed the deal.
This happens in every MMO. but in most MMOs, the endgame didn't stay stagnant for 6 years before finally evolving- it was much more gradual. the level cap rise kinda should have either happened several years earlier, or never at all. People got too attached to what they had.

You didn't see stuff like that in other games. In WoW every time the cap went up everyone happily went after the new gear- there was never this super strong attachment to current gear that there was in XI.