Most journals you pay for the right to publish. Here you are paid. Being a welcoming and supportive community like steemSTEM means the users come on their own, one small nudge to tell them it exists is mostly enough.

I like to say particle physics is an exception here. All our major journals are open access (our community is actually paying for that). I wrote about it in the past but I can't find the post right now (maybe it was a comment to some post).