PPE is designed to mitigate a completely different level and type of risk. PPE is designed for medical professionals who by the very nature of their job must spend hours in physical contact with known sick patients. The protocols must be strict because failure means guaranteed infection.
I on the other hand have no obligation to physically touch random strangers, thank god, and don’t have to go interact with known sick people. Instead I’m trying to provide some protection for myself, and trying to work in aggregate to reduce the risk that asymptomatic carriers spread the disease while doing essential activities. “Marginal benefits” in this context is also known as “reducing R0”, which is absolutely a public health goal.
Now all of that is a good argument for saving N95 masks for medical workers and relying on surgical or cloth masks for the general public, especially in the light of PPE shortages. But that is an entirely different argument from “masks don’t work”.