Not really - according to 2018 on-trade numbers, ale is 24% by value of beer sold, and cask is 55% of ale, so cask ale is just 13.2% of all beer:
https://www.marstons.co.uk/docs/reports/2018/on-trade-beer-r...
(this is published by Marston's, but i believe the data is for the whole industry)
Train passengers who want a drink are not necessarily the same demographic as pub-goers, but i'm not sure i'd expect them to skew significantly towards cask ale.
> is ruined by movement
Which is why the cutting-edge high-technology solution of "bottles" has been invented. Honestly, i find bottled beers usually better than the cask equivalent, even when i'm not on a train, i think because cask is so sensitive to keeping, whereas bottles usually reach you in mint condition. Although it might just be because the bottled versions are sometimes stronger:
https://www.adnams.co.uk/articles/adnams-broadside-cask-and-...