Social cohesion. People are happy to rip off an outsider, a stranger, a schmuck. But people within a high-trust social group generally don't rip each other off - you still need to be on the look out for fraudsters, but you won't be doing it systematically and virtually openly.

It's not a coincidence that all this has happened as the US' national identity has gotten weaker and weaker. They're shifting from a cohesive nation to one of those "it's a single block on the map but it's actually 200 tribes who all hate each other" countries, and people's values and behaviour are shifting to match.