These come in several types. The most useful ones are land developers. They buy new, empty regions from Linden Lab, which costs $375 plus $175/month, for a square 256x256 meters. There's no limit on growing the world this way. The landowner then subdivides, build some amenities, and resell. These areas are generally quite nice. It's a competitive market. The first person to own a million dollars worth of land in Second Life was Anishe Chung, who has a whole metaverse land empire.[1]
The less useful developers buy up vacant "mainland" land, on the continents created by Linden Lab, and try to rent it out or resell it at ever-higher prices. That crowd is a problem. You can see their FOR RENT signs all over. They seem to be able to make more money by not selling land than by selling it. This results in declining neighborhoods with vacant lots.
This works despite the substantial cost of merely holding land. There is a land tax, called "tier". That's what pays for the servers. Each 256x256 square of land needs about 1 CPU of a server. Beyond one such square, there is supposedly no quantity discount, although there are some "grandfathered" landowners with better rates. So it's not clear that a substantial land tax fixes this problem. If you can push up the price enough, you can still profit even with a big portfolio of unsold land.
(Most of the things the "metaverse" crowd is doing were done long ago in Second Life. Even overpriced non-copyable objects.)