>Asheron's Call, Planetside, World of Warcraft, and Dark Age of Camelot. It seems like only WoW survived

wow, daoc, runescape, eve, and now planetside 2 are still operating. everquest, the big one missing from your list, is also still online, so is everquest 2.

new expansions are coming out for everquest like clockwork, still.

UO and AC are the only actual dead ones, and they have a ton of community servers.

I have a hunch these things are cheap enough to keep going until the playerbase croaks and there isn't anyone to pay the bills left. I am sure they have very few new players.