[abdullahkhalids]

That might be the original reason, but I think that the current reason for asking for flightmode on a plane is that cell towers near airports get overburdened, as every flight would result in every phone rapidly switching between a dozen cell phone towers.

[riffraff]

I heard of this years ago, but wouldn't this be also a problem for cell towers near railways?

[abdullahkhalids]

That's a good observation. It seems it is possible to plan cell towers for this [1, 2]. But perhaps, tech has not been deployed everywhere for regulations to be changed.

[1] https://www.quora.com/How-does-LTE-perform-on-high-speed-rai...

[2] https://www.huawei.com/en/media-center/multimedia/videos/202...