So, why are they doing it...? That's the million $$$ question... Why fuck with trustees, and not individuals? Is it because the Trust adds an extra layer of protection for the trustee, so that the ATF can't just walk it back and say, "Oh those stamps are no longer valid" and then claim your in violation? Is it because the Trust is a binding legal agreement that is documented, signed, and notarized by several people, which guarantees you permission to have it? Whereas with a individual Form 4, they could just burn the whole system to the ground, and then say, "oh, we don't have a copy of your Form in our system... You must have plagiarized that, now you're going to jail for having an illegally-obtained suppressor we didn't approve..."
I mean, seems like a stretch, but they've actually done WAY worse on many occasions over the last 100 years... Waco... Ruby Ridge... etc...