I I think Galente was killed for not recognizing that he was not boss, and involvement in drugs.
I think it's possible that Galante was killed because he had a vast and lucrative heroin pipeline and refused to share it with other families. Also, Galante bragged that "I'll make Carlo Gambino s**t in the street." Not likely to win him friends in Don Carlo's family.
Ntra la porta tua lu sangu � sparsu, E nun me mporta si ce muoru accisu... E s'iddu muoru e vaju mparadisu Si nun ce truovo a ttia, mancu ce trasu.