What common factor does the group of people you describe as 'women' have?
We're born female, and among the other physical changes that happen to girls at puberty we develop breasts that can lactate - so we're women. It's not difficult.
Back in the old days feminists questioned all sorts of assumptions especially about those"biological norms". Erotogenic breasts were as open to question as vaginal orgasms. Unusual is not abnormal, and I wouldn't even bet on what is "usual".
After all these years I still despise people telling me how to be a woman.
When nipples are stimulated, they send signals to the genital sensory cortex region of the homuncular map. Our brains are wired to achieve the same intense stimulation from our breasts as from our clitoris and cervix.
There's a difference between "intense" and "pleasurable" and if it works out the same for you, that's nice. Hopefully the rest of us women can muddle along without either needing therapy or deciding to cut our tits off. Being recognised as having an equally valid ohsyical experience of womanhood helps, and telling women based on dodgy evidence that they are "the exception to biological norms" doesn't help.