There is a difference with private key and those you mentioned. If I enter some random details on a bank and successfully have access to someone's money, it will be considered illegal to move them since the person owns them, not me. The money are written on his name.

On the bitcoin world, though, there is anonymity. If you give me your private key, how exactly are you going to prove that you were the first owner of the keys? (so it would be considered that I stole them from you)