I don't use Fountain, but I think the success of Stacker News owes to the quality of the users, as well as an easy and clean interface and the ability to earn sats for an activity you'd be engaged in anyway.

Its main competitor is probably r/bitcoin, which has lower quality posts and doesn't earn you anything.

You can't easily replicate stacker.news for a community like r/estoration because the userbase isn't already onboarded to Bitcoin the way SN userbase is.

As for job markets like Fiverr, the problem is likely that the network effect is too small. Both employers and workers need a platform of sufficient scale to find good matches.