I live in America and leave my valuables unattended in public all the time. It’s locale-specific.
It’s always a culture shock for me to travel to other places in America and see bars on store windows, homeless people, signs telling me not to leave stuff in my car. I can’t understand how people let things get that way or why they allow it to continue.
What exactly are "they" going to do about it? Set up a surveillance police state where everything in public is monitored all the time, and then catch the thieves and "disappear" them so they don't re-offend? This isn't something you can easily stop without resorting to extreme policing measures. The reason it doesn't happen in Japan is purely cultural: people simply don't think to do it, because it's culturally unacceptable. It's just like pickpocketing in America: no one does it, even people who really are thieves and would steal stuff out of your car. There are crimes in Japan, but they're other kinds of crimes (usually some kind of scam). Just like there's plenty of crimes in America, but pickpocketing just isn't one of them.
It’s always a culture shock for me to travel to other places in America and see bars on store windows, homeless people, signs telling me not to leave stuff in my car. I can’t understand how people let things get that way or why they allow it to continue.