To understand the WHY you have to accept the fact that humans are just A N other animal species on the plant and the power of attraction is based purely and simply on achieving the very best mix of genetic materials to produce the next generation. This simple fact is sometimes extremely difficult for people to understand and accept.
The female, who is usually the prime mover, will seek out the biggest, strongest, fastest to sire her offspring thus giving her young the best possible start in life.
Of course as with most things in life human beings have managed to distort this simple reproductive process into the mish-mash and sexual free for all we have today leading to a gross over population of the world by one species many of whom are showing signs of a deterioration in the evolutionary process.
It seems somewhere in the evolutionary development of the human female the desire to endow their offspring with the best physical advantages has changed to being able to supply them (and themselves) with the best materialistic surroundings ...IE Cash !!!