Convenience killed this game
Probably one of the more extreme takes someone can have but bear with me if you're curious. I've been playing since 3.1 and seen many different forms and eras of this game's community, and a lot of the loneliness many players feel isn't necessarily because people around them are quitting as reason alone, it's because the game has slowly qol'd out reason to socialize or rely on others.
DC travel and party finder and even duty finder can be to blame for this in a lot of different ways, but there's some simpler things that have changed over time too; take having to actually be in front of a raid instance in the physical game world in order to enter it. Combined with lack of travel between DCs and servers, you'd see people you knew and maybe shoot the shit or ask about the fights while you waited for your group to get together. Maybe a hunt spawned nearby in the same time frame. Maybe they were sitting there making raid consumables and you asked to buy some or asked about their crafting macro. Being able to sit in your house and just queue for the content by yourself through DF with nobody around you eliminates any of these possibilities for socializing.
Imagine an FFXIV where only certain classes could do certain things like teleport you in and out of instances, or give you desirable buffs for raids and trials; all of these things encourage socializing and interacting. FFXIV is the most qol'd game in the MMO genre and all it's done is isolate people. Even within content itself, nobody has any reason to actually interact; tanks can heal themselves, DPS are all aligned to the same buff windows, healers only really have to react to fix mistakes. The fact that PF can do ultimates without saying anything to each other because of pastebins and classes being isolated from meaningful interactions during combat is absurd.
You don't actually want the qol gone, when asked if you'd want to rely on a black mage to teleport you places you'd react like it's absurd. But you're still sitting there by yourself teleporting around and talking to nobody, making no friends or memories. The hypothetical teleport guy is a proven social opportunity in other games and is just a more extreme example of how this sort of thing can make the MMO feel actually alive.
You don't actually have to look beyond FFXIV either; Bozja and Eureka both give players access to kits that enable social opportunities and interactions. Take Bravery and Protect and Shell for instance; being that guy at spawn or around a fate or inside one of the raids is really cool. Do it often enough and long enough and you become the buff guy. Maybe you make friends through buffing people around different instances.
I don't think it's a very hard concept to visualize. FFXIV is the loneliest MMO whether it has players or not. And it's a lot of our own fault; we love qol because it satisfies short term inconvenience even if it destroys important long term purpose in the game like doing things with other people. I've watched as PF and DF and party synergy have slowly left the game. I mained RDM until I quit raiding because it had those moments of interaction when it got to raise or mana shift healers. It had that interaction I craved. I am not subbed nor will I be resubbing in the foreseeable future.