A marketplace professes open standards, but it actually wants to avoid open-source like the plague. If you can trade directly with suppliers you don't need a marketplace. You still need software, but you can get that from any vendor, and the buyer and supplier don't need to use the same software. You don't need to belong to a marketplace and pay transaction fees to a middleman. Many e-commerce software vendors are talking about a shift from public marketplaces to private marketplaces.
Markets are inherently about multiple buyers and suppliers.
Marketplace is just a marketing term for an extranet. It's to save face for software vendors and consultants taking their customers down the wrong path last year with public marketplaces. Extranets have always been around. We call a spade a spade. I'm encouraged by the concept that people are saying B2B is back to basics.