Factory workers are not vetted beyond being able to perform some function on behalf of the factory owners / operators. That can be as much as having finished grade school. On your first day you have the run of the place.

> Here we're discussing a radio transmission (from what I understand) in the wild that can come from absolutely anyone and anywhere and stop a whole train.

Oh no! Such radio transmissions have been the norm for decades and plenty of such older systems are still in use all over the world. Abusing such systems is easy. Upgrading them properly is costly and carries risk so the default is to leave things as they are.

> There is no reason for this not to be secured.

Well, why don't you propose a system that is 'secured'? And then I'll show you fifty ways in which your so called secured system can be 'hacked'. For instance, pre-emptively by stealing some of the gear.

There are fall-backs for all of those and the final fall back is flares and hand signals which every railway man hopes to never see in their lives. Fucking with infra is easy. Creating systems that are still just as safe but that are secure isn't easy at all: it is impossible. As every hacked website proves. And even if you could: the next thing that would happen is that these jerks would derail the trains instead of stopping them because that too is stupidly easy.

At some point we all rely on each other not to do bad stuff.