I think the problem is two fold.
1.
How you grew up.
If you were never exposed to financial difficulties and/or managing money, then you tend to spend money without thinking. But, spending on chocolates or fries is not that expensive. When you grow up, your habits will remain but the things you buy without thinking are a lot more expensive...cars, clothing, etc etc
2.
Peer group
One can learn from making a mistake OR learning from somebody's mistake. The first is obviously more expensive in most cases. If everybody in your peer group is doing the same thing as you (i.e. point 1 above), how can you break out of the first problem? You want to be part of your peer group and will try to fit in right? It is a vicious cycle.
I have to say that I was extremely luck to have realized my mistakes when I came across MMM....purely by accident and because my mind was ready...it was searching for freedom. I paid for my late realization and learnt a valuable lesson. I also realized that there were people in my life who tried to show me this path before...but I was not ready for it at that time.
My goal nowadays is to expose people to this alternate life...whether they are ready for it, time will tell.
Thanks for the nice topic!