FF14 is great, though, as a non-MMO player. The community is largely helpful to newcomers, the story content is very accessible and requires little to no grinding, and the game as a whole doesn't gate important plot developments behind high-tier endgame content the way most MMOs do.
I think it's simply because the other CBU's are swamped with work.
- The old business division (what they called Creative Business units before the restructure 5 years ago) that made FF15 split off into Luminous Studios, and went straight from FF15 DLC into Forspoken
- CBU1 (AKA, the Nomura division) handles FF7R as well as Kingdom Hearts. Two huge franchises. Adding another FF onto the pile would be overwhelming
- CBU2 is "The Bravely division". I wouldn't be surprised if they get to try their own hand at a Final Fantasy one day, but it would have been too early for FF16. FF16 was likely being worked on before Octopath Traveler.
- CBU4 was always a smaller sort of "spinoff" studio. Nowadays they focus more on the mobile market. Very little chance they were ever considered.
I don't think Square Enix sees the last few FF games as damaging as fans do. They simply have a lot of work and some teams have more or less room for that work.
Funnily enough, it may be a possibility of FF17 having a mobile client given Genshin's success, but this is just random conjecture
Crystal Tools was supposed to make development for several games easier & faster, but instead it took more effort to complete than expected & was still difficult to work with after it was complete.
FFXIV also has the least addictive qualities of any MMO I have played in my experience. There’s very little FOMO & you’re encouraged to play at whatever pace you enjoy. Many players just play through the story and treat it as a mostly single player game.