Yeah, but the story takes no time to complete. There's no gate to get through for the story.
I'm level 50 in all crafting and gathering, and that didn't take much time with leves. So the only thing that takes time is big game fishing or trying to make a lot of gil by constantly crafting. Still though, there's no challenge in any of that, just grind & time.
(I wrote far more than I planned on >_> so here's a tl;dr: Different strokes, different mindsets. They may not understand your mindset in regards to the game just like you may not understand their mindset)
On Story: Some people are probably just doing random things while they wait for new story content.
As for being level 50 in all DoH/DoL. Considering leves take a week or two to get up far enough that you can max one class out, I would say it takes quite a bit of time.
There is even plenty of casual content for people who want gear without bothering to do coil. (Sol/Poetics), others probably just play the game to play with their friends even if it's just doing casual content (ST, dungeons, etc) without any real goal.
Yes, some people play the game without any real goal apart from playing and having fun. If they stop having fun, people can easily unsub and then resub when a new patch comes out.
At the end of the day, that's just it. Some people play the game for fun but without any real goal. That might be hard for some of the high end raiders to understand but really, it's just a different mindset within the game.
Some people also just have like an hour or two to play each day. Those people could be playing catch up for the rest of the games life considering queue times for dungeons and cutscene times during the story. Those people won't be bored yet because they don't have the time others do to play all the content every new patch. (unlike a lot of the hardcores who consume everything within weeks and are complaining about being bored until the next patch
)