The most hardline devoted communists/anarchists/etc who would be most likely to commit ideological terrorism are familiar with the historical failures of adventurism, so they don't do it. Another big factor is that corporate boardrooms, mansions, yachts, etc, are much more difficult to gain access to than driving down to the nearest wal-mart and opening fire on random poor people. Lastly I'd say people with left-ish political views tend to generally believe suffering inc death/murder is bad and are just less violent in general.

I do assume some attempts are made and we just don't hear about it though. Like, there have to have been assassination attempts by chuds on Biden (and Obama before him), right? It's just suppressed so as to not give people ideas. Stands to reason the same thing would apply the other direction.