Really is is just a measurement of how often you encounter facts. What you encounter often you cache and remember. Trivia you never use you don't.

As a 41 year old Norwegian, I have not encountered pounds often enough in my life to remember this fact.

It's not like I have ever used Google to convert either. It just isn't relevant. It is like..what is the currency of Malaysia? I really have no clue. Pounds is just something I almost never encounter.

Closest real use for pounds I can remember having I think was in "pound per square inch" pressure vs Newtons; but in that conversion there is so much else.

(Yes, before this thread I did have a vague sense. I would have said a pound was more than 200g and less than 800g I think.)