You're right, loads of publishers choose to use Amazon's printing capabilities (KEP) to manage their stock. It doesn't mean they are pirated, AI generated or self published books at all. So checking the content/ ISBN/ pictures make no difference as they use the files publishers send to Amazon's Kindle programme.
It's all about stock control essentially. As another PP said, it makes available books that have very low sales numbers which don't make financial sense to keep in print through traditional methods. But for better selling titles, it means if Amazon get more orders in than they have stock, they can print copies themselves to supply customer orders without going out of stock/ making customers wait. But as you've found, one is the issues is their KEP offering is pretty basic, the paper stock is pretty default and it can't handle special finishes, covers, hardbacks etc.
It's a delicate balance, especially for smaller publishers on consignment accounts, as so often Amazon orders way more stock than they need. Which then diminishes a publishers stock so much that they need to reprint stock in order to fulfil normal customer orders. Then sure as eggs is eggs, 6 weeks later in swoops Amazon with a big return of the stock and you have too MUCH stock for anticipated sales (which then costs publishers to warehouse). Popping a book into KEP helps publishers mitigate this.
As a publisher, there is no way of knowing if an Amazon customer will receive a KEP printed copy or a copy that was printed by the publisher. At present, I don't think Amazon has a way of flagging either, and of course, it's not in their interest to, plus they have a model which relies on making customer returning products challenging.
The only way you as a customer can mitigate this, is not to buy from Amazon. Essentially, bad quality paper can be the price you pay for the convenience and price discount of ordering from Amazon. If you want to buy online without this issue is to buy from individual websites for your local bookshop or bookshop.org (saying that, I believe they are supplied by Gardners who also use POD technology for some books but that's a whole other kettle of fish)
Hope that helps?