Unless you want to do something else and can't because people keep shooting at you. I eventually lost interest in MMORPGs such as Eve because so many players just fall into a mode of competitive hostility; I'd go exploring and on the way back I'd have to deal with piles of griefers that just sit around waiting to ambush passers-by, and fending off boredom by using multiple concurrent logins. It just becomes tedious.

I believe the main reason that Minecraft is so popular is that there are other interesting things to do besides combat.