Anti-theft isn't the reason.

Apple could easily have a dialogue that pops up saying:

"The XYZ sensor in this device is still registered to a device attached to robert8 @icloud.com. Please log into that account now to authorize the component swap".

Whilst the swap isn't authorised, firmware would power the system off after 10 mins, making any stolen laptop parts useless.

That is how it works as of recently https://support.apple.com/en-au/120610