[dathinab]

Grocery stores select which products they want to sell and have limited capacity.

Amazon provides a platform through which "everyone" can sell "anything" with no tightly constrained space/slots.

As far as I know Amazon is legally closer to a market place where everyone is up their own stand (but they are required to look mostly the same) and which happens to also require you to use their payment system.

I.e. Amazon is just a proxy while the grocery store legally buys and resells the products.