A stranger is much more likely to give you incorrect information or simply not know the answer to your question. Why bother, in the most literal sense of the word?

Why do you think it's to avoid interacting with a stranger? I have fast, accurate information at my fingertips (and it literally only takes a few seconds to take out my phone, unlock with my finger, squeeze to activate Google Assistant and say "directions to Westminster Abbey").

My phone will tell me which train to take (and which destination sign to look for), how many stops to travel, the names of the stops, as well as how long until the next train.

The OP question isn't about explaining complicated directions, just literally which way the train is heading, by the people who just hopped off that same train. "Hey does this side head towards x?" "Yep." Faster than Siri.