Having the prebuilt client and art assets you hack and change on saves you million of up front cost.

The foldingideas videos about decentraland talks about this. "Dead" mmorpgs work on a small skeleton crew despite the original game having taken 100s of people years to make. Looking it up the turtle wow server was like 5-10k concurrent players? A lot for sure but bordering on that category.

It takes a lot of work to manage that but nothing compared to making an original IP from scratch.

Don't disagree, just thinking it's a shame as it's non-trivial to create a good team that creates something new, even if it is on top of something old

Also, I'm not sure they have to start by creating an MMO