With winter here, I, and I am sure a few others, are actually sometimes wearing masks outdoors when it is not a requirement as it helps keep your face warm without needing to remember a scarf.
I'm not sure if that is why, based on my own observations, face covering compliance (everywhere, not just on trains) seems to be higher now that it was after the ruling was introduced?
Yes, they are good at keeping your face warm, and undoubtedly many are keeping them on because of that, but as someone whose nose runs a lot in cold weather, I find I have to remove mine quite quickly.