This couple that was in the same train as me, left their seats to change the diaper of their little baby.
Not only did they go away from their luggage, but they left two phones and a large tablet visible and unattended for quite some time!
You get one experience getting something expensive/cared about stolen and it sticks with you. It's part of how our brains are wired.
Just a few thieves in one area can quickly change a culture.
When i was a kid no one in the neighborhood locked their house, garages would be left open. Then thefts started happening. Garages were closed, doors started being locked. The thieves were eventually caught (teenagers turned in by their parents) but the garages have stayed shut and houses locked and it's been a couple decades.