When you go back you can gently encourage those folks to come here. If you aren't interested in modding a community here, you can ask the mods of those subreddits to start them.
There's a lot of chatter about joining the fediverse in subs like /r/RedditAlternatives, but you don't see people talking about the selling points in those small subs. You can start those conversations. Maybe there's no takers, and that's fine. But if you like it here theres a good chance others will too.
it's that dodad with the four lines above the 3 key on your keyboard