You're taking applications that are pretty inherently network-connected, like chat and sync. Yes, those make very little sense without a server. Although syncthing in particular will work just fine actually.

But a lot of things don't require internet connectivity at all, not inherently. They largely stay on one device and that's fine. If they're to be shared between people or devices, very often attaching them to an email is better than "share this link with your friends (all they'll have to do to see it is sign up for our service so Growth can report those sweet sweet activations)"