it seems like some people are able to turn off their empathy for personal gain. I bet a lot of those people you met aren't really sociopaths, after all if a harmful mental illness dictated every moment of your life, you would want to keep it secret. for example, a real sociopath i know threw gasoline on his brother and set him on fire. not something you would want to brag about. however, having an excuse for not caring about others does seem like it would get you places. i've found that once a normal person crosses the line to find out that they can hurt others without feeling too bad about it, they'll go through life stealing and using people for their own gain, and at first appearance they seem pretty well-off, if they played their cards right.
it's like you always hear from your parents, people just aren't as nice as they used to be. some of our parents would rarely lock their doors. now all you hear on the news is "be afraid of stuff! watch out for bad people!" talking to strangers is a no-no, we learn from an early age to never trust ANYONE. i've noticed the ongoing trend of increasing greed in young people that you mentioned. my guess at the reason for this is the recent development of technology that enables pop culture to permeate our view of the world. we see stars everywhere talking about vice, theft, drugs, greed, prejudice and taking advantage of others. of course every young person idolizes these very successful people and wants to take on their qualities. we learn from an early age that nice guys finish last. i believe that media's ability to show us the glamorous lives of successful narcissists has contributed to the increasing tendency for people to care more about themselves and less about others. good question.