Formatting the book is a whole lot easier than it used to be, true, but that's only part of what an editor does.
You'd think that, but I returned an eBook to Amazon after their normal return period when starting about 30% through, paragraphs breaks started being random...sometimes there would be no break in 20 lines of alternating dialog, and sometimes paragraphs would break like they were trying to be wrapped to fit a very narrow line. It also had long runs of italics (no closing tag), random font size changes, and run-together words. It was obvious that nobody had read that book after some idiot formatted it.
Also, many eBooks are apparently not sourced from an electronic copy, but rather scans of the print version, as they often have dozens (or even hundreds) of versions of the section separators (like 3 stars) as images. I can maybe understand one copy of the image, but with Unicode and embedded fonts, you can usually convert those kind of dingbats to text.
Or how about this sample (that happens a lot) of how not to do small caps to intro a chapter. The entire span is set smaller than the main text, then the first character is made bigger, and the rest set in fake small caps (by using all caps and shrinking the font). I've seen even worse examples that result in the first words at about 30% of the main font size. These are straight from Amazon, and that's exactly how it renders on a Kindle.
The author is not going to be good at reading for consistency, since the author knows a whole lot more about the fictional world than went into the story (at least, this is my experience writing stuff that isn't really publishable). A casual reader may miss a name change or inconsistent backstory. That doesn't mean that name consistency is unimportant, but rather than a skilled editor will pick up on things that will make the book worse that most people will overlook.
I can tell you right now that publishers either don't have any skilled editors working for them, or they choose to only assign them to books I don't read.
From #1 best-selling authors to the somewhat obscure, I find errors that anyone who read the book at all would have caught. Gems include sections repeated outright in later chapters (character briefly introduced, then fleshed out, but the "fleshing" used copy/paste starting paragraphs that made little sense in the later context), character name changes, spelling/usage errors (I've seen they're/their/there confusion in far too many books), and no knowledge of the character/author (character says "should of gone" as many people incorrectly do, but is "corrected" by the editor to "should have gone" in some but not all instances).
What I'm basically saying is that if you think a publisher deserves money because they provide editing for the author, much of what is being sent out by the "Big Six" shows that you're wrong.