Unfortunately the only way to change that requires work. If community is dead it won't become active unless someone will post there and we might need to be the ones to do it.

If you have some community that you would like, start posting there (if you don't know content you can copy from Reddit) as long as there is content and people interested in it, it will grow, but someone has to do the dirty work unfortunately.

In the beginning it might be better to create generalized communities that encompass multiple topics so it would be easier to find people. Not start with very specific ones. That's how Reddit grew.