Who Wrote That?

I'm not sure whether I titled this right, but I've been looking on amazon again (not at my stuff), and I've run into the "this author couldn't have written this book." And where/how/why this has come to pass in the reviews section, I don't know.
But the fact that such a comment on amazon is so widespread completely eludes me. Most of us don't have the money to share it with others who will write with us.

I don't know where the idea comes from or why it is so prevalent. Does anyone have any idea about this?

Personally, I know of only three of all the authors I know, who have had someone else write with them that are not acknowledged on the book. For two of these authors, it was a one-time deal, tragedy struck and they needed help (and no, I was not asked to give the help).

Remaining clueless...and may you have a good day today, (and bro about to turn off the electricity to mess with a ceiling fan).

Robin