That's easy. Any one can see that society demands more of women than of men. Clothing and behavioral norms are more elaborate. Women work and typically do more household chores and childcare. Younger women are expected to allow sometimes aggressive flirting. There's lots more, like potential jobs are more restricted and women get less pay. There's also a pink tax - products for women cost more.
If you see these limitations and restrictions on you, why would you go along with them, if an alternative exists?
It is almost certainly true, given that the number was "nearly zero" in the past and nonzero today. At least, the number who were willing to take the risk in public was nearly zero.
I would need somebody to present me with data to justify a claim that it's unique to girls. Most of the pearl-clutching surrounding trans identities is about trans women, who are supposedly committing all sorts of horrors like lurking in bathrooms and dominating women's sporting events.
If you see these limitations and restrictions on you, why would you go along with them, if an alternative exists?