There is a simple reason: computers and the internet. It makes people more docile and satisfies their urges. Porn for sexual urges, social media for "socializing", google and wikipedia for knowledge etc. That last part also makes everyone more educated. Which also correlates to less (blue collar) crime.
Simple and likely wrong. Violent crime started falling in the early 1990s, before the internet had much of any penetration outside academia.
A better way would be to compare what people focus on / use on a daily basis today vs in the 80s. If you are restless today you can pacify yourself with a mobile phone. In fact it's an addiction that gives you a boost of dopamine. And the virtual world is much less .... physical and violent, which reduces people's tendencies over time.
Another great pacifier of the 20th century is consumerism. Feel bad? Buy an ikea, veg out in front of the TV. There is a great documentary about how the PR industry was invented and Freud's theories about the "collective ego"