It would be nice to find out what is actually preventing people from contributing. I guess the size of the community is a big factor here but may be some other reasons?
I’d guess some people might have questions re issues in question but would just be too shy ask openly for whatever reasons. One of the reasons could be that often it’s not clear who should you ask.
A couple times I myself was in a situation where I make a PR but don’t know who exactly should I talk to about it (when no one got assigned automatically)
And then I like what @taylorfausak does with the newsletter – once I see an issue I’m like, oh, that sounds interesting. But otherwise I wouldn’t even bother going on github and filtering issues by label. Similar to how ads work.