Why do guys dislike small (A/B Cup) boobs?

I’m a girl that run a lot and do Thai boxing so I burn much fat. I have boobs but they’re so small and I feel insecure because men (especially Thai men) only finds girls with very big boobs attractive/sexy/feminine. I’m 20 so I don’t have money to do boob job and I’m scared. Should I do it anyway?
Why do guys dislike small (A/B Cup) boobs?
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