There are many different ways to approach the game, and many different things that are making people stay.
It's possible you haven't found your niche yet.

I used to play FFXIV pretty casually, only doing MSQ, side quests, normal and alliance raids.
I only started properly raiding after 3 years (didn't even know what an opener was before that), did E1S to E8S, and stopped there because it was taking a lot of my time. But I still do BLU savage raids, and recently finished all current Criterion savage raids.

I think the big shift for me was when I started looking at available mounts, minions, glamour, and titles, and started making a sort of wishlist of what I wanted to get. It started as a general "this is what I want for my character" list, but then I expanded it to have one for each job (since you can macro titles, minions, and hotbars).
As a result, to get the minion/title/mount I wanted, I had to go through tons of content that normally I would not have been tempted by.

I didn't really care about fishing, but I wanted the Sea Dragoon title for my DRG -> I leveled FSH (through pure leveling grind, no levequests) -> I tried Ocean Fishing -> I learned how Ocean Fishing works -> I joined a party to try to get the Sea Dragoon title -> I pretty much learned how to actually fish at the same time -> I got the Sea Dragoon title -> "that was fun, actually, now I want to get the rest too" -> I got all the other Ocean Fishing titles -> I started big fishing (Dragons Deep) -> I got Saint of the Firmament on FSH (I wanted the title for my AST lol) -> I started seriously big fishing -> I have all the fishing achievements and my fishing log is complete.

... All because I wanted a title for my DRG. Otherwise I don't know if I would have ever done all that, fishing does look kinda boring from the outside.

Anyway, now I'm what they call an achievement hunter lol. That's my niche, I'm a completionist at heart, I love collecting things, I love working through a big todolist, and I love customization.
Because of that, I got to try pretty much everything the game has to offer (I'm still behind on PvP and Mahjong, and I haven't tried Ultimates yet).
With every niche there's a community, so a chance to meet with people and help each other, socialize, make friends maybe (statics also help a lot with that, but statics don't have to be restricted to raiding only).

Even beyond the boundaries of the achievements menu, there's housing, gposing, roleplaying, whatever activity people are promoting in /shout, and a community attached to all of these things.

You said you liked mounts, so maybe you could also start from there? Open FFXIVCollect, see what you like, look into what you need to do to get it, learn something new, etc.