Most American Blacks aren't even actual Muslims. It stems from the NOI "The Nation of Islam", which is a non-Islamic cult that currently dominates American black's culture and politics due to their power in congress and the Democratic party. One of the reasons that Malcolm X was assassinated is because he realized that the NOI had literally nothing to do with Islam after he went there (and was probably warned that if he kept saying shit like "the honorable prophet Elija Mohammed" he would have been killed for heresy if he weren't actively on a pilgrimage"). He also realized "Elijah Mohammed" was just a cult leader, a pedophile, and a conman that had even dragged him into the scam.

When he distanced himself from the NOI, that's when they decided to kill him.