From Guns.com:

The Circuit, which controls Kentucky, Michigan, Ohio, and Tennessee, handed down a 60-page opinion in the case of Gun Owners of America, Inc. v. Merrick B. Garland this week. The crux of the issue to the court was that the ATF – effectively part of the executive branch of government – enforces laws rather than makes them, with that authority reserved for the people acting through their elected representatives in Congress.

“Congress could amend the statute tomorrow to criminalize bump-stock ownership, if it so wished,” said Judge Alice M. Batchelder for the majority, which was joined by Judge Eric E. Murphy. “But as judges, we cannot amend [the statute]. And neither can ATF. This is because the separation of powers requires that any legislation pass through the legislature, no matter how well-intentioned or widely supported the policy might be.”