Why would discoverability be low? Search engines exist. Why would contributions be low? Presumably we'd have a common way to contribute from your own federated

Why would discoverability be low? Search engines exist. Why would contributions be low? Presumably we'd have a common way to contribute from your own federated instance. There are thousands of websites (maybe even more!) and it's possible to discover them and comment/upload/whatever. Would it be better if they all moved to Medium, Wordpress.com and Facebook?