How come in every End of the World movie they cast a black president?

And its not just oh some people died, it always some catastrophic, epic form of death.

  • A meteor is  about to crash into the Earth,
  • A worldwide virus spreads around the world.
  • A nation wided chemical/nuclear terrorist attack
  • Aliens invade the planet

or some crazy shyt like that 

What are they trying to say?