Degeneration?

So what is it exactly that is going on?  If we follow the modesty patterns of people in western countries, the definition of modesty always degenerates over time.  To the point that to call the current level of dress as modest would be a joke.  So what is going on?  Why do cultures become more immodest as time passes?  It cannot simply be the ease of life.  Three thousand years ago, in ancient Greece for example, the men performed the Olympic games in the nude.  Homosexuality was common, even among married men, and there were public baths. And they didn't have the technological tools, thus the ease, that we do now.  Jumping up a bit, to read descriptions of big city culture in 1920's New York city, one would think they were reading a current newspaper.  Drugs, crime, and prostitution (both adult and child).  All the while, the latest fashions showing more and more skin and curves.
So why do we degenerate to immodesty over time?   Is it intellectual laziness, no one wants to do the hard work of thinking through implications and causes?  Is it man's inherent tendency to decline into sin?
The practical answer is that the problem is real and the Christian needs to realize that living a God-glorifying life is one that requires hard work.  Often in the face of culture opposition.  We need to learn to think through every aspect of life, to apply the teaching of the historic church to every area of life, and be willing to sacrifice every area of life to the will of God.