TL;DR The courts actually require states to intentionally create districts that have a majority population of minorities.
It's a difficult thing to manage. As a result of a Supreme Court ruling in regards to civil rights the states are not allowed to spread minority votes across district lines since it was determined that that doesn't give them a strong enough voice and doesn't allow them a united voice as well as the advancement of minority politicians in Congress.
States largely complied. But, as time has gone on people often believe that giving minorities their own districts actually hurts their political power because states put them all in their district, they get one politician and then the rest of the districts aren't a melting pot. So now there is a push to try to prevent states from districting based on racial lines, but the Supreme Court has already required them to do this. So it's a very fine balancing act the states have to go through, and in many cases they exploit the Supreme Court requirements/ruling to their political advantage.
And if you removed the racial districting you might actually lose minority representation in Congress in terms of number of minority Congressmen, which people don't want. So gerrymandering is this strange mix of affirmative action for Congress and political gamesmanship to protect a party's numbers in Congress.