Why do some women never grow pair of boobs?

was taking a lovely walk today and saw this woman running around she had sports bra on but she had flat chest like men I was stunned, why dont women with flat chest get at least push up bra like put something under the bra to make it look like you having something. Even the women with small boobs get push up bra but why dont women with flat chest do something about their chest? can't they save few bucks every month to get a boob surgery?

Why do some women never grow pair of boobs?
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