Because a racist person can be good in sciences.
The following is subjective and not proven (yet).
Talent is a particle of general human intelligence. Being good at math means you're kinda smart. It means you're smart at math. Not in everything. If you're naturally good at math doesn't mean you are overall more intelligent than a person who can't solve a complex equation. It means you're smarter than them at math. If you're only good at math and you happen to lack a significant amount of other qualities, most notable to be, being racist (not very smart), this means your overall intelligence is not that high, just a bit concentrated. If you're good at math and words and cooking and dancing and music and loads of other things, chances are your overall intelligence stands tall. I compare it to this: Every person has 100 glasses. But every person is born with a different amount of water. Someone who was born with a little water could have a bit of it in many glasses, or could have gathered it all in one glass. Just because one glass is filled doesn't mean he has a lot of water. An overall intelligent person has a lot of water, some of them have many half filled glasses and some have a few filled glasses.