Abraham, Isaac, Jacob, Joseph, Moses, Aaron – no-one objected to giving a child one of these names, but Korach wasn’t even on the agenda. Korach had such unpleasant associations that parents were simply, and understandably, scared of having a child with this name.
Their problem with Korach was not simply that he was impudent and aggressive and gave Moses no end of worry and trouble. Korach was bad news when it came to human relationships, and even worse news in relation to God.
When God had decided that Moses and Aaron were to govern His holy people, Korach decided that He had made a mistake. When God decided that Israel were to be “the congregation of the Lord”, Korach questioned His judgment. When Korach decided that God couldn’t be trusted, God decided that Korach couldn’t be trusted.
No wonder that Jewish parents didn’t even want to consider having a son with the name of Korach. No wonder they were afraid that a latter-day Korach might turn out like his Biblical antecedent.
(It is possible that similar comments could be made in connection with the name Esau, borne by the brother of the patriarch Jacob… but I did actually once meet a Jewish family that had a son called Esau. What became of him I don’t know.)