The law makes a distinction between new uses, which require certain notice to the EPA, and existing uses. The idea is that the EPA can be more aggressive with a new thing that isn’t being used yet, than an existing thing that people are relying on. That balance was written into the law.
The environmental laws are full of these frameworks that force the EPA to make different trade offs. They’re not loopholes for industry, they’re the reality of balancing costs and benefits in a country where voters will throw you out of office if gas goes above $4/gallon. You’ll never get a law that says “EPA can ban anything it wants, costs be damned.”
Inhance has been using this same fluorination process for 40 years. The EPA itself has repeatedly told companies doing flourination they’re not covered by PFA orders. The EPA changed its mind based on new science, for probably reasonable reasons. But it’s entirely fair to make it go through the processes in the law for banning a longstanding use, instead of trying to use its authority over new uses to get at the same thing.