When OpenSnitch already exists and is free and open source, a paid tool that does essentially the same thing with a slightly different (perhaps more polished) UI would be quite a hard sell.

Both for the obvious cost reason, but also because manu of us don't like having code ok our computers we can't inspect, especially not in privileged positions like a firewall is. I.e. I don't care much if a game or the Spotify app is closed source, but neither of those run privileged, in fact I run them sandboxed (Flatpak).