i think its partly because some people generally become more bitter than they used to be, due to feelings of inadequacy, jealousy, disappointment and disillusionment... they are angry at the world because they want a better life...
they see others with more stuff, better stuff, better job, better partner, better everything and they want it too... and they feel they deserve it... and then when they dont get it the seething resentment festers and consumes their whole being and they become bitter and twisted.
in the 'good old days' people were not continually bombarded with bling, massive tellys, flash cars, unrealistic looking people, etc etc - all unatainable and unrealistic goals, and were generally more content with their lot...