Because we are racist, and there is no getting around it. Nor should there be. Racism, in its essence, is the acknowledgement of differences across races and cultures. It becomes destructive when, and only when, the differences are seen as either inferiorities, or deficiencies of character. This usually occurs because of ignorance.
Admission is the first step to recovery.
We must begin to acknowledge that certain races, religions, or cultures are indeed superior to others in certain areas. Thenceforth, we can begin to respect and learn from our comparative advantages in each area. That Asians are, on balance, more adept at the natural sciences than most cultures is largely due to the society from which they come. In a similar sense, black folks have, on balance, more athletic prowess and aggressiveness that enables them to thrive and prosper an way that perhaps Caucasians lack. Today, these differences are a sore point of contention and hostility, engendering a fractious society in which polarization among ethnicities frustrates any attempt at social cohesion.