They are not. Look at the spread of skills. Then consider that some classes do not have an interrupt BEFORE you outlevel the areas.
This is important because if we played with current mechanics, you will literally not be able to do what made a lot of the fun parts, aka using your utilities. Add in the current level scaling and item level crush, plus lack of set bonuses, and you might as well ask, why do you not want to play old Azeroth with current mechanics and classes?