Why is adoption forbidden in Islam?

Adoption (تبني) is unlawful (haram) in Islamic law. It refers to attributing a person to other than their biological father, which then entails the rulings of biological sonship such as prohibition of marriage (mahramiyyah), inheritance, and kinship ties. This leads to legal transgressions like shaking hands, private seclusion (khalwah), and seeing (non-mahrams) for those who are not permissible to do so. It has been forbidden in Islam, even if these prohibitions are avoided.