Part of the problem is that editors who edit occupy a lower niche in the publishing hierarchy than they did, and they're understandably scared to suggest changes to the work of a hugely successful author. Who do you think's going to be fired if a Stephen King or J. K. Rowling book fails to sell? (Hint: who was fired after the O. J. book was cancelled?)

Also, editing takes time. Do you think Harry Potter or Robert Jordan fans (and their publishers) want the next book to be good, or do they want it now?

(I'm not a fan of either series, btw, and I'd much rather read short and good. But if sales figures are anything to go by, we're in the minority.)