Being older now (Gen X) I've noticed a change as well. I've wondered if the US culture has grown an unhealthy level of competition. Young people internalize lessons that the people around them (classmates, neighbors) are competitors for spots in prestigious programs and later, jobs. You're taught that you should be friendly, but not "too friendly" as you are going to need to be better than them to get what you want. I don't think this explicit, but something that is incentivized through grades, tests, and gamification of everyday life. That and the deepening divide between classes. If you don't get good grades, get into a good school, get a good job, etc. you may fall off the cliff into the lower classes. If that means you need to be ruthless in your social interactions, that's just the price.

It's like we've decided to let psychopaths dictate how society operates.