Why do reviews of indie books look like graded term papers?

One thing that I have noticed and am curious about is why reviewers of independently published books focus microscopically on errors, typos, and formatting. I grant you that in the flood of books now available many will have been rushed out without the introspection that a traditionally published novel might have gone through (though I wonder if that is actually a canard). However, I have noticed in my limited time on earth that professional reviewers of traditionally published fiction very rarely, if ever, go through the exercise of counting errors as a way of deciding the merits of a work. It seems, however, that it is de rigueur for a reviewer of any independent book to make some comment about formatting and/or typos even if the book had none, e.g. “I found no typos or formatting errors in this novel.” Why is this?

This is not a screed to give independent authors a pass on this very important issue. After all, if a professional reviewer found a traditionally published work to be unreadable, I suspect that a comment to that point would be made, such as, “this novel was unreadable.” I doubt that the professional reviewer would count the dropped commas, grammatical mistakes, etc., as though the reviewer were grading a college essay. I just wonder uf this is a major distinction in the way independents are reviewed versus how traditionally published books are reviewed.

I suspect that many reviewers of independent books are themselves new at the game of reviewing. Perhaps, things will change as traditional book reviewers start taking notice of the many wonderfully written books now available through the marvels of the internet.

Just my two cents worth.