Actually, transmission rates crater on their own, depending largely on the virus’s schedule. Take a look at California, where multiple control measures were put in place in June - including mandatory masks darn near everywhere - and cases haven’t responded to any of them.
That doesn't say anything about the effectiveness of masks or social distancing; it says a lot about the effectiveness of mandates. People are ignoring them. I'm against mandates, but I'm very much in favor of people voluntarily taking reasonable precautions to slow the spread.
The governors can issue all the edicts they want. This is what's really happening:
People packed in shoulder to shoulder with no masks: 
Kids packed in hallways shoulder to shoulder with no masks: 
You might as well point to a car accident where people who weren't wearing seat belts died as evidence that seat belts don't work. After all, click it or ticket, right? The mandate isn't what protects you; it's the act of actually doing it.