Cwtch requires setting up onion services, and the app currently does that automatically via establishing a control connection with a Tor process (either launched by Cwtch, or provided by the system).

Orbot can be configured to expose the same control port (or at least it could on Android when I last looked a few years back, I'm not sure about this capability on iOS), and Cwtch can be configured to use a custom control port connection - but that imposes much more work on the user, and is somewhat fragile.

That could likely be made to work on iOS in some factor, but the problem of the stability of the services themselves would remain. Its definitely something we'd like to explore.