Abandoned communities discourage interaction. While it is technically possible for anyone to post there, why should anyone want to interact with a community that's been sitting empty for two months? If a theater is abandoned, then yes, visitors can technically sit down and look at the empty stage, but why should they want to do that?

It is less of an issue if there is an empty plot that anyone who wants to actively participate can build from scratch. As it is now, people will take one look at those communities and go "eh, just lots of dead space and a mod that doesn't care, no use in staying here" and go elsewhere.

And moderating is more than just deleting posts for whatever reason. Banner, sidebar, rules, news, featured posts, advertising the community elsewhere, interacting with different instances etc. is also part of that, and a mod that hasn't logged in since the day they created their account is not doing any of these.