Why do men not conceptualize womens breasts reduce in size with weight loss?

Why is it that men have little to no knowledge understanding women's bra size is due to the overall amount of fat she has on her body.
For example a very skinny woman is likely to be an A cup whearas an overweight woman is more likely to be a D
Why do men not conceptualize womens breasts reduce in size with weight loss?
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