I'm pretty sure that the repetition in MMOs is not what most people consider the meat of the fun. It's an obstacle to get to the fun, because nobody can create enough real content to satisfy players.

The big assumption here is that people are using their time optimally all the time. I think instead we simply run out of motivation and deal with whatever is going on instead of looking for the 'best' way to have fun/work. We're familiar with it, and dislike the cost associated with finding something new.

That doesn't sound like fun, that sounds like addiction. And AIUI those games are very specifically designed to be addictive.

MMOs: not even once.