I've wondered this too. Maybe because almost all the people who have access to the carousel area are passengers with luggage. So any potential thief could also

I've wondered this too. Maybe because almost all the people who have access to the carousel area are passengers with luggage. So any potential thief could also be the potential victim of theft - and in some game-theoretic way it is therefore most advantageous for everyone to be honest. Analogous to a Nash equilibrium? Same reason why theft from tents on campsites is not (in my experience) so prevalent. Tents are vulnerable to burglary but most of the potential burglars are other campers and are therefore also vulnerable.