I just uploaded a pic of my portable CD player from 1990 to a community for CD collectors. Nobody had uploaded in a couple months and the only person who had ever uploaded was the creator.
It proceeded to get quadruple the upvotes of the last post. People are there. You just have to share what you've got.
Or if an otherwise popular community seems dead- maybe your instance just isn't federating them right, or was never federated before you browsed to it.