Literally swap the word Fediverse in that pinned post for Lemmy and you'll get more engagement with it. Because you're right, even if the current reddit user has heard of lemmy and mastodon, they still most likely don't know what the fediverse is, don't understand the site linked to is a lemmy instance / reddit alternative. Subbed to !futurology@futurology.today btw, if the current activity there can be sustained I think it'll shape up to be a nice community