[_bxg1]

Target and Walmart are not platforms. Amazon isn't the only company selling consumer goods in general (for now), but they are the only online-seller platform in their category. Shopify exists, and Ebay exists, etc., but people wouldn't put up with stuff like in the OP if those platforms served their needs.

[greeneggs]

Isn't Walmart a platform? They have similar "Sold and shipped by XXX" as does Amazon.

Random example: https://www.walmart.com/search/?query=bicycle%20tires