Dystopia

Look at Disney

Just by not doing anything actually, most boys will tell their parents that they fell in love with x girl and gave them flowers

It's mostly territorial

No, but from birth it's normal to be told that boys love girls and girls love boy, the child has all the time to realize later who he/she want to sleep with.

A me problem? Why ?

In nature you're supposed to, being able to is related to health problems. But yeah, I will raise my son/daughter in heterosexuality, if he/she wants to be gay/bi/etc that's fine. But I don't expect little boys to like other boys for example