I noticed perhaps a couple years or months ago that Amazon stopped including in their order confirmation emails the description of the products that you purchased. With pretty much every other e-tailer, I get a full description in the body of the email. It seems common sense.
I would not be surprised if Amazon did this on purpose because of how easy it is to scrape purchasing data off emails. I got this idea from this page (https://mjtsai.com/blog/2020/06/01/unhelpful-amazon-order-confirmation-e-mails/).
It is well known in stores like Target, Walmart, Costco, and even Amazon, that by seeing what the popular items are, they can easily create their own "in-store" branded items at cheaper prices than their competitors, eventually cannibalizing their sales.
With the lax security of probably most people on their smart devices, I'm sure Amazon realized that all the purchasing data could easily be "mined." Maybe by even Google themselves. Perhaps Google was gathering a huge database of frequent purchases or using it to map the behaviors of individuals. Considering the number of employees that travel between Google and Amazon, maybe an ex-Google employee that now works for Amazon informed them of the practices taking place. Perhaps Amazon knows the NSA and other intelligence agencies have been mining the data.
I recall reading that through purchasing analytics, stores are able to tell when you are pregnant with a high degree of accuracy. This is not too far fetched as purchasing newborn diapers and formula suddenly are pretty obvious signs.
If I were an intelligence agency that had access to "meta-data," I would absolutely try and gather the meta-purchasing habits from Gmail and other email accounts. Google already does this for its targeted ads.
I wonder if Google managed to target purchasing ads in the Gmail app to siphon sales away to its advertisers that normally went to Amazon. I'm not exactly sure how Amazon could measure that, but it could be a legitimate enough concern to unilaterally hide all the purchasing history behind a password system.
And, reading this additional article, it discusses it some more, but still everything is opaque, as usual, at Amazon.