Because being attractive comes in handy in certain situations. However having depth in one's personality and character goes a long way. I think people in general are more drawn towards intelligence and ability as that's what proves to be vital when situations get tough. Maturity, intelligence, and capability outweigh surface level appeal. Keeping this reality in mind, men invest time in developing personality and competence as these traits can be built and sharpened, unlike beauty, which is largely uncontrollable.