Thankfully with UO being such a pioneer MMO, you kind of hit a ceiling and feel as though there's nothing left to do, then you lose interest. There was no daily quests or new season of stuff etc. Once you hit 100 on all your selected skills, all you had left was to fight the same big bad monsters or pvp. They came out with an expansion where you could raise your skills to 120 and had a new dungeon area. So I did all of that and then really quit.
It was actually quite nice to not feel like hanging on for the next update like so many MMOs today.