Uhh.
It's a day out? Lol. I don't know tbh I've never thought about it that much. I guess there is one thing that British people like and that's British things, anything historic is legitimately liked and supported here. Whether that's things like industrial revolution era stuff or whether it's more historic.
I'd say that the train stuff comes down to Britain being perceived by the British as the origin of the industrial revolution, which is a pretty fair argument. Practically everything from that era has been very deeply engrained into British culture and identity.
Americans like American revolution and civil war stuff right? I imagine that there is a similar reason.
Also the small trains are a bit silly and British do really like silly things.
Lmao this is fantastically silly and precisely what I mean about not taking yourself too seriously being a cornerstone of british culture. Brits love this attitude, it projects a real inner-strength and confidence to be able to be this silly and authentically not have a problem with it. Super healthy behaviour.