One last try ^^^They are NOT regulated because they can be built into pistols. They are regulated because they can be built into a banned weapon. The recording of the purchase(erroneously referred to as 'registering') gives the state a date and age of the serialized lower. It's the only way the state can tell if it was built into an illegal configuration.
You can buy a dedicated pistol caliber AR lower. It is cash and carry. No 7 day wait. No 77r. You can build it into a pistol or rifle. Whatever you choose.