I've done several attempts to figure out why exactly that is - some of them in the Book Club thread, as you may have seen - but I think a big part of the reason is that I'm not a big fan of fantasy stories that are too close to historical reality while still differing from it. Rohini (Danae) mentioned Kay's tendency for big drama; when you're reading a story based on real history, and you know that history somewhat, every change and deviation comes across as having been made for the sake of increased drama, which feels rather hollow as a result. For me, anyway. I believe Jacob has similar views, it's definitely a subjective thing though.