Because our media and news systems are already sensationalized and roughly 2/3rds is fear or violence based. Folks here get desensitized and the protests are suppressed so fewer can hear about them or find them.
Our social media participates and helps this fester, numbs people where they feel comfortable - my friends and family are here, right?
Americans are taught to be proud of themselves, always act positive.
Also since the social rights movement, we’ve been financially crippled more and more with each generation due to stagnation of wages and upward movement. This makes it more difficult to step out of your pattern and pause work or life to riot because you’re trying to have food at home or pay debts out.