It’s a security thing. Would you want your iPhone to give unlimited tries where the thief will just keep trying every code? Obviously not. Hence why it’s has a self destruct option.
I understand why he stored it on there. In case someone took the usb which would of been rare but him forgetting a PIN which he set 13 years ago is more common.
Well, i might be wrong though, but for some mobile devices, like the one i currently use, i have not seen the self-destruct feature, what i see here is that, if you enter a wrong pin or password 3 times, the device will start extending the time to which it will give you an opportunity to try again.
For example, if i enter the wrong pin or password 3 times consecutively, then the device will further lock itself and ask me to try unlocking it again in the next 5 minutes, and if the 5 minutes elapse and i enter a wrong pin or password again, the device will lock itself again and ask me to try again in the next 1 hour, and if after 1 hour, i try again with still a wrong pin or password, the device will again lock itself and ask me to try again in the next 3 hours.
This can continue until it gets to a stage where the device will tell you to try again after 1 year, 2 years, even 5 years or format the device by yourself if you can't wait for that long, with a "Reset Device" button made available to you at this stage.
I think this is better than a device formatting itself after 10 pins or passwords are entered incorrectly.