...I can't but shrug upon learning that it's once again Ripley that has to be involved. Seriously, the Star Wars universe is so vast. There's so much potential there, so why it has to be always about Skywalkers?
I feel like there's a connecting sentence missing from the middle of your post. The mundane reason is that the book would sell less well if if wasn't about Ripley, so we've mostly got ourselves to blame.