Average users do not even remotely care about federated software and/or decentralisation. That is techno-babble to them and their eyes will glaze over if you try to market that to them.

That being said: Mastodon does a shit job at explaining how it works, how to use it, and what its advantages are. The Joinmastodon landing page just assumes you already know how a fair bit about instances work and what federated software is and does a very poor job explaining it. And even then, most users won’t care either way. They just want to click a Join button and be done.