I get the impression that fractions are very much engrained in American psychi and cultural identity and thus is a strong influence for opposition to a metric system.
People in these threads talk about 1/3rd of an inch as if that’s a real number :)
But seriously I think you are right. I never use fractional notation or thinking when I’m building something, while it seems very common when reading US sites. I have a socket set which US Customary sizes in fractional inches and mm; I cant tell which of the US sockets is bigger without comparing them, but 11mm is obviously larger than 10mm (to me).
I think your observation about cultural identity is spot on, but as always it goes both ways - I think the US system is nuts because of all these crazy fractions.
Until now I didn’t realise that this was my own cultural bias against fractions leaking in.