Markets are unpredictable. I doubt there's much wrong with the Amazon phone, and it's not like it has a problem Blackberry has - that they may go out of business and you'll have an orphan device, so it seems odd that it's selling so poorly.
By all accounts, Windows Phones work very well, but it's not selling well either, even though they are generally less expensive than their competitors.
I think it's all about perception and recognition. People got familiar with phones from Apple and Google/Android, and other phones just don't register, no matter how well they might work.