Marketplaces are a great place for consumers and producers to come together online. Across industries, dual-sided marketplaces have untapped latent demand or better utilized supply and created really interesting businesses along the way.
As marketplaces grow, consumers come to expect the benefits of economies of scale - better selection, price and overall fulfillment experience. As producers become more savvy, they will want to exercise more control over the entire customer experience. Ultimately, as entrepreneurs, most of them will want to own that customer relationship themselves.
This creates a choice that defines the identity the marketplace - to focus on building the largest end-customer base, or to focus on helping sellers become the most successful. There are of course examples where building for both can work for an extended period of time, but managing equlibrium is incredibly difficult as marketplaces scale.