You understand that propaganda costs money (and by extension, a person's time), right?
The right has all the money, the left has none. The right has the backing of big media empires, the left has none. A lot of us on the left are too busy just trying to survive in this capitalistic hellscape, and even we did make some "counter-propaganda" as you say, it certainly won't be picked up by the media and/or it won't be taken seriously by an already brainwashed audience.