That's really not true for the type of game the OP is talking about. Think Second Life et al, where most of the content is dynamically streamed and rendered in real time

We're seeing more real metaverse-type systems. With the NFT clown car out of the way, and Meta's Horizon becoming a niche, the development efforts that were quietly underway to build real, working metaverses are starting to show results. There's M2, from Improbable, which now has a shared developer metaverse in test, for which one can sign up. There are others who have reached the demo video level, such as Readyverse, which is probably going to be an MMO rather than a real user-created metaverse. Disney and Epic are jointly making metaverse noises.

The big-world high-detail user-created metaverse problem is being worked on.