Many pioneers who had their $Pi stolen claim that nobody had access to their passphrase. Well, the irony is that a thief will never announce to you when he gets access to your passphrase otherwise you would already be expecting the theft.

Just because you were sure that no one got access to your passphrase doesn't mean that that is the reality. Your $Pi cannot be transferred without your passphrase to open the wallet, and you're the only one it was shown to when you initially created the wallet.