There's a book called Designing Virtual Worlds from 2003 that might be interesting to you; since it's 2003 it predates World of Warcraft and some of the information is dated, but other elements are timeless. It was re-released under a Creative Commons license in 2021:
https://nwn.blogs.com/nwn/2021/08/richard-bartle-designing-v...And another recommendation if you're interested in worldbuilding is the Encyclopedia Eorzea books from the Final Fantasy XIV game, three of them; they contain the full backstories, timelines, summarised in-game stories, locations, characters, races, etc etc etc. However, it's written "in-universe", not so much from a developer's point of view.
That said, you didn't specify which part of said games you would like to read about, I can imagine more information about the design and build would be interesting too, a look behind the scenes. The video game resources I mentioned get you there partway though.