I think people are every bit that competitive, if you put a group of strangers in a room it won't be very long at all before they're sorting themselves into a pecking order. Perhaps subtle things like judging the car you drive, the fashions you wear, asking what neighbourhood you live in, what job you do, where you were educated, etc. The point of politics is precisely because people are competitive: to subvert the Prisoner's Dilemma that arises in an anarchy. People generally vote for the party they think is acting in their own best interests.
You have to ask why people keep consuming more and more, but not getting any happier, especially now that we can see the environmental damage that is making it contrary to the common good. I think Miller has it about right: a combination of status competition and the denial of habituation.
Habituation
The brain has evolved an ability to adapt to it's environment, therefore the nervous system will generate a response when the stimulus is changing, but not with an unchanging stimulus. A simple example is to hold a tinted cellophane sweet wrapper over your eye, and watch the way that the colour you see gradually fades after a few minutes. Take it away, and you see the complementary colour until that fades too. Or watch this. It's the reason why people may feel suicidal after an accident puts them in a wheelchair, but not after they've had time to adjust, and why people can't smell their own BO, for example. But it's also why an elated lottery winner doesn't still feel elated a year or two later, why people aren't still excited by new purchases a few months after they've bought them, and why the poor aren't impressed when they're told that they're better off than their grandparents were. They judge their wealth relative to that of the peers who live in the society they're habituated to, not that of previous generations.
When you drive to the car dealers to trade your car in for a new one, you are full of excitement imagining how much better your commute will be in the new car, but you have completely forgotten that you felt the exactly the same way about the car that you're sitting in when that was new. Habituation means that the satisfaction of a new purchase doesn't last, which is why increasing wealth produces no more happiness in the long run.
Lack of public toilets in towns.
Passports not in the drawer I always keep them in. Turning the place upside down.