I recently watched videos of Bernie Sanders, who americans call left-wing, and maybe compared to other american politicians he is, but compared to russian opposition he is very like Boris Nemtsov and Alexey Navalny. First is literal founder of Union of Right Forces, second is considered to be center-right.
Decades of anticommunist propaganda, destruction of the careers of communists via McCarthyist red baiting, and in the worst instances outright murder of prominent leftists. Like if I went to a communist rally with my face uncovered and it got sent to my employer I would probably lose my job.
We're talking about the democrats though, the "left" party with actual power, but the most radical among them are social democrats at best with most being centrist technocrats. There are genuine leftists and even left parties in the US but none with any power.