I mean, it's not going to be as successful now as it was back then by any means though.
It was not only a new game, but it was also a novel idea to many people in general.
A lot of other MMOs were too hardcore and/or nerdy to be popular with the general population. Blizzard, at the time, was really the company that took a lot of these nerdier and more hardcore games and made them palatable for the everyman. So not only were MMOs somewhat newish in the general timeline, but they were also likely BRAND new to many of the people who only really played Blizzard games.
The novelty of the concept of an online chatroom that allowed you to physically interact with other people was definitely a large part of WoW's early success. It's not really a novel idea anymore.