It's not even the "did not end well" part. People would be reluctant to jump over to a new MMO regardless of FF14 state.
There are plenty of people who stayed with WoW for two decades through the thick of it - it's not like they didn't have their "it's looking bad" moments. Attachment to the community, friends and characters mean a lot. And new game is a new game, regardless how good or bad the predecessor was.
