Although it is not easy to guess someone's private key, if you guess someone's key, then you have become its illegal owner. Whether the asset is stolen or found on the street, you are not its real owner. Now you have mentioned one point, now if the real owner of a wallet dies, then his children or his heirs have the right to claim it, but you cannot become its owner by guessing it. If you do this, then it will become illegal.
I don't remember my own key, sometimes I make a mistake while accessing the wallet. How can I guess someone's private key there, ha ha.  

Any wallet containing coins retains its rightful owner, even if someone manages to guess the seed phrase. Bitcoin wallets differ from bank accounts, where the bank provides legal safeguards for account security; Bitcoin wallets operate without a third party, meaning individuals are solely responsible for their own private keys. If someone accidentally guesses the seed phrase, they could transfer the Bitcoin and claim the funds. They might well avoid legal repercussions, as tracing the person who guessed the phrase and took the assets would be extremely difficult. In fact, many wallets remain inactive for long periods because the owners have disappeared or completely forgotten about them—implying that someone who successfully guesses the seed phrase could possess the coins without fear of legal action. Nevertheless, both morally and legally, I consider this an act of theft.