Why is it that when a woman has or wears something, it keeps its normal name but, if a man does, it HAS to have an M instead of its normal letter?

Women:
Sandals, panties, pantyhose, brassier, boobs, etc..

Men: Mandals, Manties, Mantyhose, MANsier, Moobs, etc..

And, why it is that, if a woman wears or has something a man usually does, the names DON'T get changed?

Why is it that when a woman has or wears something, it keeps its normal name but, if a man does, it HAS to have an M instead of its normal letter?
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