Oh, you wouldn't believe the really odd freaky ways snow and ice can disturb operations of basically anything. Some examples:

- Driving through powdery snow you get a huge cloud of very small and light snow particles. These will acumulate in the weirdest places on the undercarriage of a train, in ventilation slots and basically into any small crack where normal, plain water has no chance of ever coming. (The bodywork is designed so a drop of water will drip off the train, not dribble into cracks. Powdery snow flies everywhere you don't want it). If that doesn't disturb some mechanical operations or short circuit something electrical then the repeated melting and freezing caused by running in and out of (relatively warm) tunnels surely will enable water to short circuit something or ice buildup to disturb whatever mechanical.

- Frost on the cable will impair the connection between the train and cable.

- Any rubber-like material such as gaskets and seals will become brittle in the cold, so they won't work as intended (unless you use the right qualities).

- Any plastic will become brittle and may break (unless you use the proper materials)

- Huge temperature differences between the inside of the train and the outside means that most places in between you'll get plenty of condensation, as water or as frost. Think of how many that have trouble with their car doors when it's cold; a lot of those problems are due to condensation.

- Any door has a rubber gasket that can freeze so the door won't open (prevent with silicone grease!), and any door has a door lock that can freeze.

Robustifying against all and any places where powdery snow, water or condensation can cause trouble can be done, but it is typically fix-this-wait-for-next-problem kind of process. Not really difficult, but it takes time and effort.

Cars seem to have converged on a design that is pretty much robust against the effects of winter(with the exception of door locks for A LOT of car models), but a train has a lot more nooks, crannies and weird places for snow, frost and water to accumulate.