In the book Satisfaction, Gregory Berns argues that too much of a good thing can make it less good. For example, sushi is his favorite food, but if he ate it every day, it wouldn't seem as good. Part of what we crave is variety. So it's not just avoidance of displeasure that keeps us from doing our favorite thing all the time, it's also our craving for variety. I enjoy skiing, but I also enjoy great food, movies, and art museums almost as much. I'd rather spend my life doing some of each of these things, rather than just skiing all the time.
It's an interesting question. A few different responses were given. I'll go with the pain/pleasure ration. Doing something has to have a lot higher pleasure than doing the much easier alternatives. This is rarely true so we get stuck in a narrow band of nothingness.