"Always" a lie? Prior to the 1900's initial feminist movement, after a divorce, the children went to the man in almost all cases because, surprise, he was considered the more skilled and able to provide and raise kids, all other factors being equal. It is specifically thanks to first-wave feminism that the courts redefined it so that women would be given priority in a void (and even well beyond it).

It has only "always" been a lie for about a century, the most recent century, and the era of postmodernist philosophy and the takedown of stable society.