I think that's one approach, but many other federated systems don't do this. ActivityPub does not do this really, instead Mastodon, a product using ActivityPub, markets itself. Arguably you could look at HTTP and say that HTTP doesn't have a fancy landing page pitching itself to users, browsers have landing pages pitching their experiences to users.

Matrix could have a fancy landing page pitching itself to implementers who implement homeservers, bridges, or clients, and they could market to end users.