It wouldn't surprise me if these steep fees hit many different types of publication. I think that many people seem to forget that there are many different types of publication, and the responsibilities of the copy editor will vary according to the type of publication. Copy editing for a novel is going to be fairly light weight compared to a non-fiction book for a general audience. Copy editing a non-fiction book for a general audience is going to require less effort and fewer specialized skills than an academic text. Clearly you aren't going to pay the same rates in those cases.

Is $10,000 reasonable? I don't know. I've only done copy editing once, was paid hourly, and it certainly cost the author in the thousands of dollars. That book was at the border of general non-fiction and academic.