Pharma companies they're insider trading on get money from it. Also puberty causes children's brains to develop at the same time as their bodies and if it is blocked by endocrine disruptors there is marked loss of intelligence and ability to think critically. It suits a government that wishes to become more tyrannical to have as large as possible proportion of the populace be easily-influenced, low-IQ, and stuck at a stage of development in which reliance on authority is neurologically hardcoded in. Or pedos in high places want underdeveloped people that are technically legal age and have been fed media diet of deviant hypersexual weirdness for years. Take your pick, there's a load of possible reasons, none of them good.