I mean honestly, it’s a “fact” that has been perpetrated since early 2010s (if not before) but I’m struggling to see how it’s supposed to be recorded. Its not the census - which if anything should ask BMI; but it doesn’t. You can’t do it based on viewing a person as a 16 looks different between someone 5’ and 6’. It could be average clothes sales - but it’s not hard to consider that someone at a larger or lower size buys a lot in one go to accommodate their needs - so essentially it will always be skewed.
So, my TLDR - AIBU to suggest that we need to rid ourselves of the ‘average size is...’.
I feel like it’s time to stop thinking that an ‘average’ dress size is even a thing. People are not sizes, and sizes mean absolutely nothing anyway. It’s just another means to validate or shame people with an arbitrary number.
[as an aside, men do not have an ‘ideal’ dress size and as far as I’m aware, I don’t know of any existing ‘average men’s sizes’ “facts”]