It is definitely a big downside for a lot of people, yes. And looks like you understood just fine, if you look in the sidebar of that politics community as viewed from futurology.today, the subscriber count reads 0 (because it also only shows the sub count from your instance). That’s why new posts aren’t being pulled in.
I’ve seen various discussions among server admins of how to handle it, I think some use a bot to basically sub to everything as a workaround to populate the All feed without real users being subscribed. If your server has a meta community maybe you can ask around there whether they’re planning on anything like that?