I imagine most reviewers don’t accept self-published works because of the perception that most of them are unpolished and of poor overall quality. Which has a definite basis in fact; these days you can get self-published in minutes if you go to the right (or wrong places) and the lack of quality control means there’s a lot of crap out there. If I was a reviewer, I wouldn’t want to waste my time on a book that could be absolute drivel.
I don’t think that does a fair service to the ones that stand out, though. Plus, though many self-publishing firms are vanity presses that will print absolutely anything without caring about the quality of the content, some do have decent quality control, and offer at least basic editing services to bring their books to a minimum level of quality.
Quill definitely does. The crowdfunding model alone serves as a quality control measure; good luck getting 250 people to buy a book full of basic grammar and storytelling flaws. Not to say that hasn’t happened, but that’s why even Quill books get some help with editing.
I’ve read enough inkshares books now that I’ve found ones I like and ones I don’t like, but never have I read one that seemed unworthy of published status. I can’t see why any respectable reviewer would have a problem with the books we produce.