Simple reasoning. We know that viruses can be transmitted through saliva. Covid-19 generally presents with a cough. Coughs aerosolize saliva. Wearing a mask or face covering catches most particles, and absorbs energy from all particles, so they dont travel as far. Less virus mass, and a smaller projection plume will result in less spread. Less spread results in a lower R0.

I realize that you are just enjoying being contrary here, but please try to think through your argument and ensure it isn't incorrect in itself before posting.