It's to try and separate bigotry and racial management, orientation, and distribution of a society.

In fairness, the Left used to use Racism as the latter. But they subverted the individual bigotries of people so much, that the term has become synonymous with simple bigotry.

They wanted to argue that the individual perceptions of one person were the exact same as a structural form of racial control and manipulation, that people accepted the simple definition and forgot about the expanded implication.

So, I use Racialism to focus entirely on that expanded implication: A genuine system of racial management.