There are multiple reasons why FFXI still entices me over the years.
I've tried every MMO out there to compare
*Guild Wars 1/2
*AON
*WoW
*Arch Lord
*Black Dessert Online
*FF14
etc...
The fighting mechanics of FFXI are the best I've experienced. It's almost like removing the jump and dodge feature that is so common in all makes it better, even though you'd think it was worse. The game UI is just much easier to navigate than others. I am not overwhelmed but the amount of macros, plugins and addons which in some games are required due to the amount of skills you are provided.
FFXI is becoming more close to this as of late, but gear in other MMO's have so many stats its hard to keep up.
Graphics in FFXI are still high-tier, but there are better. WoW looks like N64 and even with maxed out graphics just looks "cartoony". I like a little more realism in my game, if that makes sense.
I am also biased as FFXI was my first MMO. Those who played FFXI first tend to hate other MMO's. Those who didn't play FFXI first tend to think FFXI is 2nd to most.
The game won't die, as long as they keep adding new content, entice newer players to come back with the addition of increased EXP, trusts and uncapped missions. SE isn't going to retire off of the monthly subscriptions going forward, but the game will be respectable in the MMO community and will continue to live for a long time.