I thought that it is the the skating federation of the country where the GP events takes place who decides who they are going to invite. There are some rules within which they have to choose (seeded skaters - at each of GP event is one from 1-3 place from last worlds and one from 4-6 places, also the priority of skaters according to their past results), but otherwise there is a big space for manoeuvres and tactical selection. For example, if they have strong category of their own skaters (like Japan has ladies and men, Russia has pairs), they can choose tactically and invite weaker skaters; if they have no contender, they can choose the best (to make it better for the audience). I did hear that the seeded skaters can express some preferences, but I am not sure if everyone always get what they wanted. The weaker skaters are glad that they got anything, so they definitely can't choose. The only choice USFSA have is about who they send to skate America, so your suggestion USFSA is racist because Mirai has been to CoC four out of five times, and NHK one out of five is ridiculous. The most likely reason why she was sent to CoC so many times is that Chinese ladies are weak, they have no contender of their own (in ladies), and she skated well in the past so they wanted someone strong there to draw in the audience.