i think richard's twisted behavior is all a result from his father's 'brutal training', so...

I think it’s a combination of:
1: emotional neglect
Nobody ever actually cared about him as a child, person, or family member so he obviously wouldn’t be able to understand or model empathy or care in his general life.
2: the burdens of being royalty
He knew from a young age that he was being raised for the sole purpose of relieving the king of his rule so he could dedicate his life to his deceased wife. On top of that, he has no siblings, so zero chance of passing it to someone else