Earlier quoted context omitted.
Macbook sure, phone maybe, but why would your watch be in your backpack? Also, the watch automatically enters a locked state when its off your wrist.
Because the robber said "your Apple gadgets or your life!", and carried them away in the bag. Or, perhaps because you put in in the bag to go through airport security, and the bag was handed to someone else.
Your phone is locked because its got TouchID enabled and a passcode.
Your laptop is locked as well. Getting in here requires you unlock something first, even if you have everything. The stronger security devices provide authentication to the weaker ones.