Do you mean because they're poor? There's plenty of poor people in Japan, but they don't resort to stealing people's phones or wallets. Again, it's cultural. And it's not just America; over in Europe where there's a far better social safety net than America, petty theft is commonplace, especially pickpocketing (which, to America's credit, is almost unheard of there, which again shows this stuff is cultural).
Pickpocketing is only a concern in tourist traps like if you went to visit the tower of Pisa out something.
And waking around my university buildings, it's very common to see people leaving their stuff including expensive laptops to reserve their spot in the library and random tables in hallways that have them. Though this is frowned upon if you're going for more than a few minutes.
> Pickpocketing is only a concern in tourist traps
I have not spent a huge amount of time in Europe but judging from the way certain minority groups are spoken about by many Europeans, it is not a widely held belief in Europe that pickpocketing is limited to tourist areas - although I'm sure that's mostly true.
I’m saying it’s not because we’re not “teaching” people not to do it, or not telling them not to do it, like the parent comment says. Of course we tell everybody not to steal. Clearly telling and teaching are not the gap here.