We've created popular culture that doesn't value intelligence. This has an intergenerational compounding effect. When smart people aren't socially valued for their intelligence, they mate with less attractive people, and the effect is reinforced in the next generation.
The opposite is happening in India. Intelligence is a high ideal, and seen as insurance against abject poverty. Men with prestigious degrees and good careers regardless of their attractiveness generally have their pick of wives through arranged marriage. This ends up resulting in a lot of people that are both intelligent and beautiful, and the preference for intelligence is reinforced.