Exactly this. Also airport employees have been known to open luggage and help themselves when out of public view.
Like most Americans, I don't pack anything in checked luggage that I would cry over losing. Plus baggage is insured by the airlines and most CC companies.
Even if passengers hit a restroom after exiting the flight, most arrive at baggage claim several minutes before the bags start coming down and watch the luggage chute with eager anticipation. The thief in the video grabbed bags from a nearly empty carousel - no people waiting and only a couple of bags remaining.
The big advantage to having luggage on the public side is that passengers can get assistance from porters or whoever is picking them up from a flight. Still, your point is well taken,
@hollydolly, and if I could wave a magic wand over US airports, I'd have baggage claim moved to a secure area. Unfortunately, the cost of reconfiguring a large US airport to move baggage claim would be astronomical.