This probably would need to be in a separate discussion thread on its own, but I find part of the issue XIV and their content become stale quickly is the level of vertical gear progression that they chose to go with.
Each major patch brings us a new tomestone, where everything else is instantly outdated and obsolete. We normally get 2-3 new "expert" dungeons, a new 8-man raid, and down the line a 24 man raid. The pattern is stale and predictable. Sure, we visit old dungeons now and then, but I think most of us probably only ever see them when doing our Roulettes as there is very little reason to ever go back -outside of helping new players or glamour.
Touchy subject around these parts, but XI had a massive amount of gearing options and end-game variety by this point in it's life. At 4 years in, they had just released their 4th major expansion Wings of the Goddess. I'm sure I'll probably forget something, but that means gearing could be done by Dynamis, Assaults, Einherjar, Limbus, Salvage, Sea, Sky, Nyzul, ENMs, BCNMs, ZNMs, etc. The fun part was that everything was still completely relevant, even the events that came out that first year. Reason being - horizontal gearing. Gear had very specific stat and various skill boosts - so you would want to collect specific pieces to buff certain actions and abilities.
Now, obviously XIV is a completely different game, and they've gone down a very different path. Just pointing out that not every MMO's content is outdated the week it comes out

It's amusing to me how SE has gone from creating one of the more challenging MMOs, to creating one of the more simplistic ones. Just looking for some middle ground here.