The editing process can sometimes be quite demanding for both editor and writer. The author has made the text as good as they can – perhaps having edited it several times already, and she may have also used a critique group and beta readers. Now we’re asking her to make even more changes.
The editor usually sees things the author has not noticed. Even so, there is still the possibility that she may be stuck in a rut or cramped by a house style that has become formulaic.