While you may be right regarding the context in which you said this — satellites — as a blanket statement, that's not true: my smartphone loses Internet connectivity when I leave my house, and takes a few seconds before it connects to the cellular data network.

I'm surprised that phones don't establish a backup 4G connection when Wifi signal strength decreases suddenly, but before it disconnects. This has been talked about for years, but for whatever reason it hasn't been deployed or doesn't work well, at least with Android P.