Thats because people are not self content and look at what others have, humans are naturally competitive and want more (greedy).
We are violent and aggressive if we do not get what we want, people say they are not however, but yet they look at helping others as a chore or in hope of something back from someone else,very rairly do people do completely selfless things.
We naturally want what others have that we think will benefit us for the better then comes the part of competitiveness, whether it be for jobs, money, fast cars, a stunning women etc etc its all quite simply in our nature. To obtain these goals we must maintain the competitivness with aggression, for example can anyone honestly say they turned up for a job interview or whatever and saw another candidate for the job and thought well i dont need the money just let them have the job because the other dude looks like he wants it? A really nice bloke who wouldnt harm a fly will still be competitive.
Next comes the part of playing sporting, for this we look to the law and our morals and say ok we are not going to shoot or kill the other candidate but we will look at their flaws or weakness as we see them and play on that once again this is aggressive stance to the competition.
To go back to the original post more people living close together in for example citys see more of these 'wants' every single day where as people who live more isolated lives see less and dont 'want' as much (of course until they see these things then they want them to).
So to try and sum up i just think that humans can adapt and do it very well whether it be alone or in groups i think it comes down to the individual what works best for them.
