This is not true. Applications only require network connectivity for the initial resources to be downloaded. After that they can be cached, service workers can

This is not true. Applications only require network connectivity for the initial resources to be downloaded. After that they can be cached, service workers can also be used to provide for offline support. Plenty of applications can run only in the browser and don't need to have a constant connection to a back-end. I can think of a calculator app, where all of the application logic exists on the client in JavaScript, in this case a network connection is an unneeded dependency. But once you build it with a framework like liveview it cannot work without a constant connection.