If you can't find a reason to log on, then you simply don't log on. And sometimes I think people expect full blown expansions with the release of a patch. I'm new to FFXIV, but have a couple other MMOs under my belt including FFXI, and it is nearly always the same for vet players who are fed up.

I think nostalgia is the biggest culprit here. I feel the vet players continuously seek out the experiences they had when they were new players, but this just isn't possible. You can take breaks, and even play another MMO for a while. You will do so to no avail. You are only a new player once. You can experience the game's content for the first time only one time, and there is so much fun in learning how things go. And the suggestions that are often given are frowned upon because most are basically asking for a new game, or the current game to contort to their standards.

That doesn't make it ok for designers to remain complacent with the vets, and I can't really speak to say if they are or not. But I do know that if the above statement applies, then it is perfectly understandable why it is so difficult to sustain the enjoyment in playing the game.