I'm only aware of open bazaar but with open sea, why it is on number 1 on your article? And the same goes for the origin protocol. I don't know these marketplaces that you are suggesting.
Why not include the forum's marketplace categories? there are a lot of trades that's happening there.
A marketplace is a place where you can exchange crypto for products. Don't think about it as a place you exchange cryptos as that is more of an exchange concept.
Opensea - You can purchase ERC-271 tokens (items on the blockchain)
Origin Protocol and Open Bazaar - You can get items for your crypto.
I know about what a marketplace is but what I don't know is the existence of the other two marketplaces that you have mentioned. The idea of opensea is like the digital goods of the forum's marketplace to make it easier to understand.
What I'm questioning here is that why is it that many haven't heard about those marketplaces that you have included. Yes, open bazaar is quite popular but the other two is what makes me wonder.