What gives us legal ownership over our wallet?

Since all wallets already exist and I just access mine with the matching randomly allocated seed “keys”, what gives me more ownership over the wallet than somebody else who “discovers” or even outright steals the same key? Is it even stealing if I didn’t own it in the first place since the wallet always exists and I just happen to be the first one to use it?

There is no registration or account creation or anything like that for a wallet, so where the point where ownership is legally recognized?

Edit: Some interesting replies so far thank you! I understand that from a technical perspective, it is not your keys not your crypto. I am more interested in the legal ownership, which I also understand is very nuanced since bitcoin is global.

I’m really trying to understand in general if you are in a legal jurisdiction that recognizes theft, and somebody was able to get your keys, and moved all the bitcoin out of the wallet, would you consider this as “your” bitcoin being stolen? If so, what is the basis of ownership?