Apple hasn’t yet figured out how to stop people from selling their used equipment.

Many Apple products are bought from third party resellers who don't capture this information.

That's not relevant to the case at hand, where OP was actually able to prove that he'd originally bought the device.

And the owner could have sold it and stolen it back in in the many months he have bought it. I guess if you manage to block the device in the store itself, they will unblock it for you - but it would defeat the purpose in this case.

They have to work on the balance of probabilities though. It would be very long odds to sell a device, steal it back, then need to approach Apple for help unlocking.

They can't rely on the odds, because scammers would step in and increase the odds if the possibility existed to exploit Apple's behavior. IMO, this is what should happen given that Activation Lock is enabled.

It's a separate question whether the customer should be able to disable Activation Lock before it gets tripped, which would prevent the computer from bricking itself. Apple makes that choice for the customer because they don't fully respect your ownership of the device that they made.

This is the dumbest argument.