Definition of racism inconsistency?

I can't find [the superior/inferior] requirement anywhere for any definitions of similar words in any dictionary. [...] Is there a reason for this?

Yes, that you haven't looked hard enough.

Sexism

• The belief that one gender is superior to the other, especially that men are superior to women. YD, TFD

• The belief that one sex (usually the male) is naturally superior to the other and should dominate most important areas of political, economic, and social life. DR

• Refers to the belief or attitude that one gender or sex is inferior to, less competent, or less valuable than the other. TCDoPCC