Knocking the achievers down because they can’t bring the underachievers up.
It's the same logic as economic Marxism: their programs can't lift the poor out of poverty, but they can sure impoverish everyone else.
Interestingly, one way in which Communists in the Soviet Union and its satellites differed from Western Communists is that they did make an effort to maintain high academic standards. Rather than "everyone's a winner," the attitude was that those who did well in school could become engineers or scientists, those who didn't would go and dig ditches and mop floors. Today's Leftists don't even seem to grasp that concept.