Are PFAS's a by-product of stuff like teflon and plastic production and the like? I know big oil is evil but I'm not sure that they're the boogieman in this case.

In this specific case, no they aren't the main villain. They are more the catalyst that turned the republican party into the anti-environment party (and thus anti-clean water).

The EPA regulating PFAS means it can also regulate the effects of fracking.

That's the context to understand how Republicans went from the Nixon party who created the EPA to today's party that hates all parts of the EPA.