There is a great comment I read about a decade ago from anthony_franco [0] about exactly this issue with many "open source alternatives to X", this one specifically about an alternative to Product Hunt that then failed:

> OpenHunt tried solving a problem for the content makers without providing any additional benefit to the content consumers. It's a nice, heart-warming mission. But in the end of the day, content is king, that's what consumers want.

> There have been many examples of people rallying around a "free and open" version of a service. They fail to realize that the end consumer barely cares. Look at voat (Reddit), app.net (Twitter), Diaspora (Facebook), even ycreject.com (Y Combinator) tried to be a thing for a while.

> If someone is able to make it "free and open" while also making it a better experience than the alternative, then it'll be a big success. But so far everyone gets that wrong.

[0] https://news.ycombinator.com/item?id=10934465#10940729

The elephant in the room here is how you ethically get people to onboard without an existing community / fomo / money.

The trick is getting the content creators there, but most of them are ultimately and fairly interested in making money, and your new platform wont have that for them.

Bluesky has done alright, but that was a black swan event Elon Musk inspired.