This makes it a perfect tool for judging someone's character.

That's true! I definitely think that more people put them away than did when I was growing up. Especially the younger generation as @daltono commented. It is interesting to see how not a single person in my comments has admitted to ever not racking their cart. Haha! Perhaps those who are into cryptocurrency are more conscientious than the general public. I have to personally admit that there was a time when I would sometimes not put my cart away properly. But I NEVER once just left a shopping cart free flowing out in the middle of the parking lot like I see people do these days. What the heck? It is worse than lazy, it's like you said:

wind might blow a cart into another car and damage them

I have definitely seen this happen before.

This social pressure might be what caused the actions you saw in the UK.

Well said! That is a very good point. That is really how I was trying to describe the way people behave in England in general but I couldn't think of a good term to describe it at the time of writing. Sometimes social pressure can be a bad thing, such as when religious bigotry or racism becomes a norm. But when it drives beneficial behavior it is great!