When choosing what TV show or film to watch, most of us probably think our main consideration is something other than how "hot" are the actors.  Not so, apparently: 

As an acting coach, I’m writing specifically about actors, who today are being cast more and more on their looks and less and less on their talent. … Where once casting seemed to strive for a combination of looks and talent, the equation now appears to have shifted radically toward the former, particularly with regard to film and television aimed at the youth market. Not long ago, I coached a young woman on a screen test for a television project. Afterward, the casting director told me that she had been "hands down the best actress of the bunch" but they had decided to go "another way." "Why?" I asked. "Because the girl we went with is a Victoria’s Secret model," he said, as if that were the most obvious explanation imaginable.

As in most industries, the main expense in giving shows is labor, and the most expensive laborers are actors.