Sadly true. There have been games with large, seamless, 3D worlds combined with multiplayer for a long time (late 90s at latest), but almost all new games use some combination zones (e.g. shared spaces, but broken up), or instances (spaces shared only with a small group), or phasing (spaces shared only when you're in a similar game state), or the Destiny-style "we'll have people show up whenever we feel like it" tech. That last one seems hugely popular these days, to the point it's showing up from the other direction -- other people showing up in your single player game.

I think it's because of a combination of technical difficulty and game design reasons dealing with overcrowding and camping and other bad behavior.

And I also think it's a total cop out and decimates any sense of "place" in these games, which I think is so important in games like these.

If anyone has examples of modern games that don't do most of these these things, I'd love to hear it. I'm not up on all of em, particularly the ones in the primarily Asian market.