Imagine saying that to every ticket holder on the train. Every day.
The main reason train conductors say ‘Thank you’ is not only to show they care (although you could argue it’s desultory) but also to mentally check a passenger off the list. It also triggers the passenger to put away their ticket. Relief.
They say to practice speech in front of a mirror for a reason. We remember what we say better than what we think, more so than inner monologue. But we really remember our lines when we speak with emotion, as do others when we say it to them.
That’s why the monotone ‘Thank you’ is such a practical and word, a paradox rife with boredom.