The prostitution/ sex trafficking industry and Big Harma are behind it. Two powerful Capitalist Patriarchal institutions stand to gain by exploiting the bodies of children. All the land and natural resources have pretty much already been exploited and the only thing left for them to exploit are the bodies of human children.
It's a two for one deal - fuck up kids heads and make them hate themselves and think they need to by polysexual and give sex to everyone. Make a realistic sex change prohibativley expensive. Tell kids they can do "sex work" to pay for it. All corrupt patriarchal institutions benefit from it. Kids being happy and gay don't make any profits.