Well, it was kind of the only game in town. Sure, you had Dark Sun Online and Meridian 59, but in 96/97 you were playing UO if you liked the idea of online worlds.
I think the barrier to entry is the equivalent of several complete, fun, balanced single player games operating together in balanced harmony. Not impossible, but highly improbable.
Btw, I've never met a player of Meridian 59, but seeing YouTube videos about it, it might have been popular in my community if we had access to it at the time. Looks super interesting, although it didn't age well, of course.
A big cluster of my in game UO friends had come from playing together on M59. Just like we view UO to have been ahead of its time, the stories they told me made it feel ahead of its time back then. It wasn't *that* different from the MUDs of the day, but more video gamey, which was a big step up
I think the barrier to entry is the equivalent of several complete, fun, balanced single player games operating together in balanced harmony. Not impossible, but highly improbable.