The vast majority of demons never leave their subspaces, even though they may live for countless hundreds of years. Ever since the introduction of plentiful food, and the equally important introduction of nearly the entirety of pre-(H)istory media and entertainment, they are content to eat, socialize, and relax. Although a demon has no natural lifespan, they do have a more or less mortal memory. This means that after seventy or so years they are very happy to begin again with old movies, tv shows, books, and games. This cycle can repeat indefinitely.
The ones to watch out for are those with the deep desire for power. But here we have our strongest, if unwitting, allies in the form of the Demon Masters. They have carved out a place at the top, and they are more than happy to crush any who dares rise too high.
-Notes on The Age of Sloth, by the Highest of Angels