"If Virginia has one of the lowest rates of new cases, why are more restrictions necessary?"
I don't think it matters how South Dakota is doing when considering how well Virginia is doing. It's not a competition and no one is being graded on a curve here.

"And with so many people wearing masks, why are the number of cases increasing?" Why shouldn't cases be increasing? Cases merely need to be increasing more slowly than they'd be without masks for masks to be effective. They don't need to be perfect to be good.

I'm not sure where the idea that masks would be a perfect solution came from, either. I don't think anyone suggested that. Things with, for example, a 10% chance of happening, happen. Still it's better to have a 10% chance of loss than a 20% chance of the same loss. Masks aren't perfect, that doesn't mean they aren't good.

If you think VA needs to do better than VA is currently doing (again, someone else can argue over that), then more restrictions are how you do that. If you are getting C's showing up to class and the goal is an A, then maybe you should study too.

Also, I'll point you to the other posts pointing out how the originally linked summary of the study contradicted the actual study.