How come some Women gets F size boobs?

What could be the reason? Genetics or too much hormones or Weight gain, lifestyle or something else?

I have seen some women including My Mom too and Now its a Big reason of having back Pain to her ALL the Time with No Permanent solution other than to a breast reduction Surgery which is definitely Risky and Expensive option !
How come some Women gets F size boobs?
How come some Women gets F size boobs?
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