Because in this game, we are able to do everything one one character. On any other game you have the ability to gear up every character. They all have their own weekly "point" caps that they trade in for gear, and you could do all of them every week if you had time.

In this game you can totally do the same, you just need to do it on another character. But why? In a game where you can do everything on one character, why shouldn't we have a separate caps for each class? It would literally be the exact same thing as leveling that class on another character and gearing it up on another character.