I had a similar experience trying to report a product that extremely misrepresented itself and yet had ~5 stars from reviews that were obviously assigned from an unrelated product.
My impression is that Amazon doesn't want to know: good reviews, fake or not, drive more transactions in the short term.
That seems very short sighed of Amazon. The viability of Amazon's open marketplace depends on the review system. Once all trust in reviews is gone people will increasingly shop somewhere else (whether that's a shop with more reliable reviews or one that carefully selects what they sell)
My impression is that Amazon doesn't want to know: good reviews, fake or not, drive more transactions in the short term.