We live in an unfortunate reality. A reality where success is measured by an entity's collective will as to its continuation. Humanity is an organism the likes of which this world has never before encountered. We have studied the makeup of our bodies and the world they thrive in so we might be better prepared to prosper in another world of our own construction. We understand that our very being is the end result of molecular communicability between our component cells. In that same way, we communicate with each other. We teach and learn and reproduce, every time teaching our youths up to our current level of discovery with the hopes that they will move beyond mastery over the known and into understanding of the unknown.
Our particular genetic code is well-suited to survive in our universal environment because it builds us with intelligence enough to question that environment. To improve it, to move beyond boundaries so that the human organism may flourish, growing to spread our reach as far as possible.
Our universe is unstable, we know this. Thusly, our humongous sense of spite compels us to avoid such a dismal fate. How to do this? Continuation. Each member of our species believes (rightly so) that their particular genetic traits can be useful in our society's future. So each member of our species finds the task of an equally endowed mate to compliment our favorable genetics, and perhaps negate those that aren't so. People are smart creatures. We are shown something and either immediately or through regular interaction are able to discern the positive and negative traits of the thing. We're shown a potential mate, and looks are the initial reaction. A phenotype, however, does not ensure favorable mating. The initial yes/no of one's interest in another weathers prolonged exposure to the other's personality. At that point, the initial response either remains the same, or is changed.
In summation: why do we find someone beautiful? Because our instinctual mind believes that certain phenotypes are more worthwhile than others to pursue. Why does society place beauty in such high regard? Because society is little more than the current human gene pool's phenotype, and our collective instinctual mind believes that a successful human appears a certain way. Just as we want that same look for ourselves, it follows that we want a better look for our progeny. And just as society understands that it wishes to expand its boundaries limitlessly, it also understands that such a task becomes easier if each member is striving for perfection. So the interest in the discovery and exploitation of perfection is promoted, not because of any particular man's agenda, but because of every particular man's agenda.
I hope the few of you capable of thought required to read this post in its entirety enjoy any thought it might provoke.