From Apple’s side, this situation is indistinguishable from the phone having been stolen.

P.S. Although maybe there’s a way to learn to what account a part is locked, and write to them ‘hey bro, could you please unlock this phone you threw away’. Then again, the repair shop also can’t know that the phone wasn’t stolen.

The internet doesn’t stop existing when your phone breaks.

Ask the previous owner to remove the locking, same way as they would need to if you bought the device to use it. What’s the problem?

Again, says right there they should just remove the device from ‘Find my’, which disables Activation Lock, the very same feature that prevents theft for reselling the device for regular use.

Instead of using Repair Assistant to unlock the part, you can remove Activation Lock using Find My.

Sounds like this is to prevent theft for parts. Considering it says right there that parts can be unlocked with the user’s account. So it’s the same mechanism that makes a stolen iPhone non-functional unless unlocked by the user.