This is particularly true for shamans and conjurers.

I can't think of any way I'd naturally have rot at say, 85%, or for that matter conjure archon (by the time I'd want to take the skill), given you only cast it at most once every half hour or so of playing once you reach the level you can cast it.

Barring level gain improvements and such there's a lot of skills that just don't go up very quickly.