The thing is, you have to take the complaints with a grain of salt and recognize them for the vocal minority that they are. For starters, only a small fraction of the playerbase even posts to the forums or even to the subreddit. A lot of people don't even know they exist. Then you get into the fact that people that are enjoying the game don't generally come to the forums to post about it. They simply enjoy playing it. Most people only post when they have a question or a complaint (aside from screenshot threads and "show your glamour" threads and things like that, which are in a cool little category all their own).
In any case, I'd like to see some kind of proof for the claim that "most" people that take a break from a game don't ever come back to it, because it's my experience that most of them do come back at one point or another. It may be weeks later. It may be months later. It may only be temporarily, but the fact remains that they do tend to come back. My ingame wife is a great example - he let his sub lapse back in October or so because he just wasn't feeling it anymore, and he came back in March to check all the new stuff out. Some people simply have cyclical interest in games. Other people tend to play one game to the exclusion of all others. FFXIV is great in that it's accessible to both types of players because it's very easy to catch up.
Then you move on and find a new FC or LS if you wish to keep playing and want to have people around to do stuff with. Clinging to a truly dead FC because you don't want to leave those people behind (when in reality they have already left you behind when they left the game) is just punishing yourself for the sake of old memories. People quit and move on from games all the time due to various things, whether it be because they don't enjoy the game anymore or because something in their real life changed. The very few people I know that have flat-out quit the game, it hasn't been because they wanted to or because they were tired of it; it's been because something had changed with their life and they no longer had time for it.