Originally the idea was intended to provide and more equal representation.
In a dense urban setting, the different minority groups tend to cluster together but those clusters rarely follow any kind of orderly district lines. In a randomly divided district, the minority groups are often in contention, so usually won’t vote for each other. This means that the the winner tends to be the white guy. If instead, you shape the district to follow the different clusters, then each minority group is much more likely to be able to vote one of their own into office. Unfortunately, the rules that were created to make things better for minorities were also able to be weaponized against them and eventually against the majority itself.