So, I can’t speak for others, just on my own perspective:
FF14 is just a ‘different’ kind of MMO. It is more of a visual novel, extremely heavy focus on the story, and gameplay is just a vehicle for that.
WoW, is the opposite- gameplay is first and foremost, story is an afterthought.
During SL, both the gameplay and story were so hated, people wanted to show Blizzard they still wanted to play MMOs but just not WoW.
There was a mass exodus, I was a part of it, and tons of “WoW-fugees” found themselves learning and playing FF14.
Honestly, it was a good move- I learned that an MMO could actually have a good story rivaling even triple-A single-player RPG games.
Right now, FF14 had some hiccups because people didn’t like Wuk-Lamat or whatever one of the new protagonists is, and said the story fell flat, which is pretty bad when your game is known as ‘that story MMO’.
But overall? FF14 is fine. It’s a juggernaut just like WoW is, with a lot of diehard fans that’ll stick around until the servers go down.
I personally came back to WoW, because I love PvP, and FF14’s PvP just doesn’t do it for me.
I actually did enjoy their PvE a ton though, it’s really spectacular.
Both games have a different ‘feel’, and you can’t really describe it to someone who hasn’t experienced it for themselves.
It is like explaining wine to someone that only ever drinks soda, lol.