You're betting on the fact that there will never be an event where a malicious party comes in contact with your phone. Which might very likely be the case, but it's not a non-existent risk.
A phone screen lock is a low friction, low cost solution for mitigating that small but impactful risk.
I think dolmen was saying that if its likely that a phone can be found after being sucked out of an airplane, a scenario like yours is also prone to happen
A phone screen lock is a low friction, low cost solution for mitigating that small but impactful risk.