I think what’s scaring a lot of people off is moderation. I’ve considered creating a few communities myself but I’ve never been one for managing. I try to do my part by interacting with communities that have been created and driving activity. Huge kudos to those who are founding these communities though.
Just do it! It takes about 30 seconds to create one. It's going to take a long time before these communities, especially the more niche ones, require full-time moderation. Something like AskLemmy might be a big undertaking, but other niche subs are going to take awhile before it's too much for one person.
And hopefully by that time, others could help out with mod duties :)
I did that twice on Reddit. One time, the sub was flooded with spam and adverts. 90% of posts were ads from the same commercial account. The second was overrun with hate speech and threats and I just had to shut it down (admittedly it was a sensitive subject at a heated time).