I'm more than capable of recognizing someone who is smarter than I am, and as a rule of thumb I prefer to work with people who are smarter than I am.
Also, as mentioned above, it is harder for many B-level people to recognize and value an A level person in the hiring process. An A may come across as arrogant by describing things as good or bad to a B when they're simply knowledgeable and confident because of that.
There were some A programmers at Amazon, and they were respected, but they weren't the ones who made the hiring decisions. Since any B or C can veto any hire, A people often didn't get hired in favor of B or C people. (and A people who already worked there, eventually, got excluded from hiring loops because they're "needed elsewhere.")
prevents B players from hiring A players
Ego and in a big corporation, the fear of the hire going ahead of you.
Also another deadly combination is the B player who hires another A player thinking they themselves are A+ player and spoils the fun for everybody.
there is some research that shows that your own competence directly affects how good a judge you are of your/others relative competence, i.e. people who are low competence will rate themselves routinely as 9-10 / 10 but people who are high competence will rate themselves 5-6 / 10 ...