weights and measures

Why is it common for people to give small item weights (wheels, bars etc)in grams but overall bike weight in pounds?
I was taught both at school but find it easier to judge weight in metric. I dont have a problem measuring distance in imperial though.
Just an observation as its quite regular to see it here.

I often measure things in both [at the same time]
i.e 4’7″ & 3mm or 6′ x 35cm

work for me

yeah, I can see how that would work, just dont understand mixing weights.