Earlier quoted context omitted.
> Note that the reason for airport mode is a courtesy to cell-phone carriers. This doesn’t track. What about trains?
You're supposed to put your phone on airplane mode in a train or subway too, but most people don't: https://pocketnow.com/airplane-mode/ The problem is significantly lessened for trains vs. planes though because you're traveling an order of magnitude slower and hence you switch cells an order of magnitude less frequently. Also many commuter rails run alongside major highways or boulevards, where the cell systems are…
Millions of people travel long distances on trains: 353 million/year on the Shinkansen network, 1.5+ billion/year on China high-speed rail, 110 million on France's TGV. These passengers use their phone without overloading the cell networks.