It's strictly a function of funding and the economic power of the interested parties. Rich capitalists are, naturally, invested in promoting policies, ideologies, and politicians that will 1) keep them being rich capitalists and 2) make them richer capitalists. I don't know, but am fairly confident in stating, that there are not rich communists waging a communistic propaganda campaign in order to keep them being rich communists and making them richer communists. Certainly not in the Anglosphere, anyway.
You’re not wrong, but leftists also tend to spend an inordinate amount of energy and resources fighting internecine battles rather than trying to convert others. This does make it rather hard to do things like run self-reinforcing YT campaigns, assuming YT would tolerate them.
