Communism was the system used* by the US’s primary geopolitical opponent for generations as well as its current economic rival. Meanwhile fascism is/was considered a long-dead ideology by most (American education doesn’t really focus on things like Francoist Spain), even while support for it among the capitalist elite has been quietly simmering in the background since the 1930s if not earlier.

*Nominally, but let’s not get into that.