You are correct that the ATF will make up their own rules for whatever they want, but the case regarding the 80% makers was that they were selling a "full kit" of everything, which meant only a little bit of work was needed to make the gun. This shouldn't be illegal at all, but in this case, it wasn't against Brownells or PSA or anyone selling lower part kits, etc. It was a fully stocked kit with an included 80% lower.