I shout and gesticulate at those who nearly kill me, so it seems logical to acknowledge those who show me some consideration.
I’ve noticed myself doing this, basically you’re publicly thanking someone for not killing you and you know, treating you like a fellow human being*, makes me cringe every time I do it, but hey ho, you need to reward good behaviour when you are training good behaviour into kids, animals and simpletons
*I’m thinking about someone not racing you to a pinchpoint or going to left hook you then slowing down and waiting instead, you know common decency