When the second flight is due to go, there's the problem, there are cases onboard with no passenger,
In the US in August my bag went on the flight before me out of DTW to BOS as I had a long-ish layover. No danger as it had been screened. Was quite happy that it was waiting for me before the plane was unloaded.
It's a simple way of making sure some idiot doesn't get on the wrong plane!
Well if you keep treating us like morons don't be so surprised we get flustered and occasionally lost....