But seriously not to answer a question with a question, though I am going to... but maybe the better question is "why do frameworks like Backbone need to use jQuery?"
Base angular is incredibly compact and I have yet to really run into a wall with it compared to projects we have tried to do in Backbone (that sounds like we have had problems in backbone we haven't I am just saying the experience is comparable). It seems to me like the best reason to keep jQuery in something like Backbone is to make it easier to integrate existing jQuery libraries... which is maybe worth reconsidering anyway.... see argument #1