That said, i think it should be pretty easy not to tease or shame children for being friends with the other sex.

I think a lot of parents of young girls are terrified that their kids will be attacked by young boys. So they cloister them deliberately.

A lot of parents of young boys are terrified that they'll turn out gay. So they pressure them to be toxically masculine.

And gender neutral clothing costs the same as gendered clothing

They're significantly cheaper, by and large. But by the time you're dealing with teenagers, they're largely dressing themselves.

Try to explain to a 15 year old that he shouldn't be emulating hyper-masculine/feminine media personalities.