15 jobs that you cant even use in endgame because you are limited by the amount of stones one can farm.
I am not saying that artifact searching is for everyone. It was an example on how to make more use of the zones. (And in rift you do get some stuff out of collecting a whole set of those artifacts) I know that not every content is for everyone but if you create more and more of different kind of content you will reach more people that have more to do. If you have someone that loves the lore you will keep them quite busy if you introduce lore books ingame in all the zones, dungeons and more. Or make it sellable so people can farm this for Gil if they have no interest in the content itself. Gear and best weapons are also not always the best kind of carrot on the stick which can be seen in the new diadem.
At least in real life you normally dont go that often to themeparks thus they stay fresh for a while. I am really not sure if a themepark kind of thing is really that great for a MMO where you want people to play constantly (or at least pay their sub). So you play it a lot to get your money out of it thus if you have the same "ride" all the time it will get boring quite fast.
The problem is that SE often does not have a good balance between it being too easy or getting stuff nerfed or making it way too much of a grind. Its fine if stuff takes some time (I am slowly building my wins to get the Feast mount) and maybe its okay if there is some RNG in it but then you will have achievements like the tiger mount which will take years if you did not already do a lot of hunts. Or you have weapons like the ones from Diadem that are beyond such a huge layer of RNG and on top of that in boring content, that nobody wants to even truly try it. If you make it too much you will just demotivate people to even start it. Or you just nerf everything to the ground and give everything out like candies thus people just dont feel the need to work towards it when it was fresh. I mean is it truly necessary to put Materia, pets, glamour clothes behind so many contents that they are not even worth a bit? Its okay to make it easier over time but they also overdo it in that aspect.
So you will have content that is not that fun with items that you will know will be nerfed anyway..so why bother? And you have content that will take you such a huge amount of time and luck that you also wont bother. (I am looking at you TT...which I would have loved to get..until I saw all the horrible restrictions and RNG that you need..thus one needed to constantly do it to even get a chance at owning them all..or cheat in tournaments to get certain ones)