[logicalmonster]

I'm sure that poverty can play a factor in worsening social trust, but can the reason for anything as complex in society only have 1 cause? Also, arguing your point, there's far poorer countries that are far more trusting. And arguably at the US's "poorest" (maybe during the Great Depression to WWII period) there was a much different social attitude to strangers than exists now.

I'd say that commenters have brought up some good factors like mentioning the media's business model in hyping up negative clickbait, but personally I'd say that the increasingly heterogenous population is closer to the biggest factor. Identity politics drives a wedge between most groups that can tend to make you distrust the motives of almost anybody, even if the stranger is a member of your own group. As long as identify politics persists, countries with an increasingly heterogenous population will have even lower trust.