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)
That doesn't mean the coins on the address are any less "mine", just because they are not attached to my real name. By that logic, Sstoshi doesn't own a single satoshi. What if I find a briefcase with a million dollars in cash on the street? I don't require to break in anywhere to take it, and there is no name attached. That doesn't mean I can legally keep it.
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)
I could provide a zero knowledge proof that I am in possession of the extended private key or the seed phrase which was used to derive that private key.