In message , at 11:49:33 on Mon, 3 Apr 2017,
Martin Coffee remarked:

If a train is stranded without a functional driver then the situation
can serious especially if the signalling is such that the signaller
doesn't know exactly where the train is. I dread to think what might
happen if this is somewhere without mobile coverage.

It's a balance between what might go wrong once a year, and the cost of
all those guards.
--
Roland Perry