Imo, it's because they don't really solve any of the issues around systems that do keep players subscribed and playing. You wanna decorate houses and play around with that system between patches? Better get one somehow. You want to collect glamours and make outfits? Limited slots there and tons of arbitrary limitations, sorry. Even the achievement system seems to be mostly forgotten about by the devs.
One of the easiest things you can do to keep people engaged and playing is essentially collection/decoration type stuff, but the FFXIV devs just kind of refuse to acknowledge/address it and have for a decade. It's a shame too because the long term stuff like this we have is pretty close, but they just seemingly don't care to put that last 10-20% in to make them actually good. They just kind of called it good enough and now they just joke about it on the live letter instead of doing anything meaningful.
Actually, I actually think the "good enough" mentality kind of defines the last few years of FFXIV to me.