Here's how it went down.
So last April-May, I built a chrome extension that detects fake reviews on Amazon. It analyzes a combination of factors about the linguistics of the review (part of speech tags, unigrams and bigrams analysis), the reviewer metadata (rank, percent helpful reviews, number of reviews...), and the overall product reviews statistics (standard deviation, percent one time reviewers... etc).
At the end the reviews quality are scored on all these factors to give the product reviews a letter grade rating where "F" means that the product is very likely to have gone through a reviews bombing campaign and an "A" grade is for a product that contains mostly reliable reviews from reliable reviewers.
On the side I've been applying to Amazon jobs, and the last one I applied I included in my resume that I made such an app. About a couple of weeks later I get an email saying I was lined up for an interview. The interview went OK, I didn't do great in it to be honest, I didn't do bad either. I got asked about the chrome extension I made to describe what it did and why I did it which I obliged in answering.
Two weeks later, I contacted them to know about the hiring process and I got a reply that I was not considered for the job and that they couldn't share the reason why.
That sucked. What stung me even further, and made me believe that the interview was only a sham reason to only know about my app, was the fact that the product that I used as an illustration on the chrome extension store got banned. Not only that, but multiple products from the same seller and other sellers in that product category engaging in review deception schemes also got banned or more in their lingo "Discontinued".
BUT the app still detects products with deceptive reviews in other categories so it wasn't a site-wide update.
This is my story. Do with it as you wish. And be careful in dealing with large corporations.
Edit: Here's the link to the chrome extension in question:
https://chrome.google.com/webstore/detail/evalute-amazon-reviews-le/cfngaogeljebhifobnjlhoakgaogmndj?hl=en
Your interview might have made them acutely aware that your extension exists and they may have either got a copy and looked their site's products to find issues or at least take care of the "low hanging fruit" examples you used.
So what occurred might have been as you say. And I suspect you didn't move forward on the interview process BECAUSE of your extension (i.e. they didn't want to muddy the waters in case Amazon's legal department wants to send you a C&D letter) but I don't think they needed to interview you to get intelligence on your extension (since any engineer worth their salt at Amazon could have told them the same thing, just by downloading a copy and reading).
It sucks that Amazon didn't see the value of your innovations and exploit them to make their site better. But their loss I guess...