Because as an adult I'm happy to have a female body- like, sure there are downsides, but on the whole who wouldn't take multiple orgasms, longevity, ability to bear my own children, soft hairless skin, nimble fingers, long legs, plump curves...
And as I've aged I've embraced more of the stereotypically female traits- I cry easily at sentimental stories and over animal welfare, wear makeup and heels, sew and knit and garden and practice yoga, am naturally submissive and enjoy following a male partner's lead.
But I feel that if I was growing up these days I'd struggle with gender identity and go down the path of presenting as non-binary or male, try hormones, go to therapy, etc- and that my life would've been worse for the struggle.