I guess it depends upon what you mean by complex. UO was a 2D world, MUDs are text worlds, and modern MMORPGs are 3D - that right there is going to make any gi

I guess it depends upon what you mean by complex. UO was a 2D world, MUDs are text worlds, and modern MMORPGs are 3D - that right there is going to make any given feature more complex in a modern MMORPG than UO or a MUD. What I think they mean is MUDs and early MMOs were more sandbox-style. This can create complex and unplanned interactions in the game. But the market has mostly decided they don't like these style of games. So you won't get a AAA developer making them because the money just isn't there. Many people loved these interactions. But even more hated them. These days you have options. Back then you didn't. Back in 2000, if you wanted to play an MMO, you had 3 options. Nowadays you have dozens. MUDs also have the benefit of not having millions of dollars on the line. And a million monkeys typing all at once. There's literally thousands of MUDs out there. Most of them are really bad and uninspiring. It's funny to think about how things have shifted. Back when WoW was released, instancing was controversial. Some didn't completely consider it an MMO because it let you opt out of a shared experience with others you don't know.