Except Amazon started as a third-party marketplace. This isn't *new*, some of us just have really short memories. For the first several years the only first-party sales they did were in books (and not all books on the store even at the beginning). They've expanded into other first-party categories, but there are much fewer first-party categories than people assume. (And always have been.)
The big thing that changed isn't the third-party marketplace on Amazon, it's that they increasingly and intentionally blurred the lines between "third-party" and "second-party" marketplaces. Any third-party that uses "Fulfilled by Amazon" logistics (warehouses, shipping) just about gets automatically upgraded in the Amazon user experience to "second-party" even if Amazon has no deeper working relationship with the third-party than "Fulfilled by Amazon".
Some of that intentional blurring of the lines is also questionably Dark Patterns intentionally designed to confuse consumers in just exactly what categories Amazon supports directly (first-party) and which ones are third-party, and more importantly which ones are first-party usually versus third-party today (such as sold out goods). They want to give consumers the illusion of an "everything store" that is never out of stock. That's never the practical reality, and the illusion may be evil from the perspective of shadily pushing consumers to unvetted third parties due to Dark Patterns that back that illusion.
The big thing that changed isn't the third-party marketplace on Amazon, it's that they increasingly and intentionally blurred the lines between "third-party" and "second-party" marketplaces. Any third-party that uses "Fulfilled by Amazon" logistics (warehouses, shipping) just about gets automatically upgraded in the Amazon user experience to "second-party" even if Amazon has no deeper working relationship with the third-party than "Fulfilled by Amazon".
Some of that intentional blurring of the lines is also questionably Dark Patterns intentionally designed to confuse consumers in just exactly what categories Amazon supports directly (first-party) and which ones are third-party, and more importantly which ones are first-party usually versus third-party today (such as sold out goods). They want to give consumers the illusion of an "everything store" that is never out of stock. That's never the practical reality, and the illusion may be evil from the perspective of shadily pushing consumers to unvetted third parties due to Dark Patterns that back that illusion.