Its like you start a new game and it has a bunch of classes.
You keep wanting to try them all out, see what they can do.
Eventually you played them all ... but that feeling of wanting to try new classes stays with people. Some more than others.
You get prestige classes or special classes or combo classes or hybrid or kits .. anything to keep the treadmill going.
But designing new classes that work inside a game that was designed without them? That's not as easy as it sounds.
In COH we have ATs that still need fixed (Khelds, Sents) Powersets that still need fixed (EM, etc) and so on.
By get over it, I didn't mean never should there be another AT ... but I did mean if you try to add them to keep people happy, you will never add enough, and most of them will be badly designed.