In the story, passengers are reluctant to dismount their coaches because they do not relish the idea of waiting for another tram while stranded outside in the cold. Furthermore, the unrelenting cold is usually accompanied by strong winds.
So, the passengers usually refuse to disembark unless a fire on board threatens their very existence. Even then, they often wait until circumstances leave them in no doubt about their danger before they climb out. The passengers know that most trams are packed; therefore, the chances of being picked up by another tram is very slim. Furthermore, some passing trams may be in disrepair and so, cannot pick up any passengers.
The passengers reason that, even if a tram leaps off the rails (due to the recklessness of the driver), other trams will soon be along to help 'haul it out.' They prefer to wait in the safety and security of the tram rather than risk being stranded out in the cold, with no prospect of continuing their journey.
The reason for this reluctance to dismount is that the nights are howlingly cold, black and windswept, and a car is a haven of refuge. From village to village the miners travel, for a change of cinema, of girl, of pub. The trams are desperately packed. Who is going to risk himself in the black gulf outside, to wait perhaps an hour for another tram, then to see the forlorn notice 'Depot Only'—because there is something wrong; or to greet a unit of three bright cars all so tight with people that they sail past with a howl of derision?