I play Everquest, i'm a long way into the game too, however it is a very expensive pursuit. Sony release expansions at an alarming rate (2 since christmans) and ontop of the account subscription that sure adds up, doubly so for me as I run 2 accounts at once (I have two hands and 2 computers so why not !?).
The game is extremely shallow and the AI more primitive than a bemused slug. So why do I play it?
It's a social game. I've met friends through EQ and gone to wild parties (well 1 wild weekend and 1 hello how are you) and i've enjoyed the time i've spent chatting to people. I've even met a Yank who came all the way over the pond just to meet the gang. Many of my RL friends are EQ players (friends from before EQ I should stress, and a few new friends since).
The game itself is a bit like playing pool in the pub - it's a distraction whilst socialising and gives a common topic to chat about whilst you break down the barriers.
As for writting one, i'd actually love too and feel more than capable of doing so.
However the big barrier for me is server support. To run an MMORG requires a server which requires funds, needing funds meens you must charge players money and that meens the server must run 24 hours a day which meens it needs someone watching it 24 hours a day... You also need to maintain and update the product itself in order to maintain your user base which is creatively limiting.
The financial commitment to maintaining an MMORG is huge (from the point of view of a non-professional programmer) and one that I am not able to make.
If I was, i'd already have written an MMORG. Infact a game i'm working on right now could work pretty well as an MMORG with a quick plot change and a few new models.
It's not terribly hard to write one if you consider the application properly and set about what you need to do in an organised method such as writting your movement code to be network-game friendly and so on.
EDIT: PS, I'm Pneumatic Dryll, a 59th level epic cleric with 10AA on the Xev server. My name is in no way a crude and immature suggestion of extra-marital procedures.
If you do start EQ i'd recommend the Xev server because the high end guilds get on well with each other making it a friendly place where co-operation is in place of disputes and because of that Kerafym is unlikely ever to be awoken. (significant once you get to the end game).
Pneumatic Dryll, Outrageous epic cleric of EQ/Xev
God made the world in 7 days, but we're still waiting for the patch.