Hollywood was in fear of him. Back then most of Hollywood leaned towards Socialism/Communism. Too bad he really did not dig them out completely.
McCarthy was chairman of the Senate Committee on Government Operations as well as its Subcommittee on Investigations from 1953 to 1955. They never investigated Hollywood. That was done by HUAC.
“Back then” understates the continuum that continues to this day, of course. There were still a small number that weren’t communists, like today.