Looking at the local timeline of functional.cafe there is hardly any tech related toots, much less functional programming. Is this expected of Mastodon networks? I noticed the same thing with bsd.network.
Jokes apart, I'm trying my best to make it a more technical instance, but I can't control what the users toot. I just hope that someone joins a tech instance to talk about tech...
I'm @loke@functional.cafe, and I certainly post about other things outside my main programming interests. So far no one has complained about that.
I think the point of an instance with a topic has more to do with the fact that people on that instance tend to be people with similar interests to you, not that every single post is about that topic.