The ATF is not intruding into the business of architects by having their buildings registered under the NFA.
Note carefully how they are NOT in charge of range construction, which when properly done does suppress the sound of gunfire. No authority exists in their charter to examine building drawings and conclude a firearm shot thru a combination of ingress/egress openings and interior partitions constitutes the use of a suppressor.
Not to forget every pillow made and sold in the United States would require an NFA stamp. As would any blanket wrapped around the muzzle, or coat, or even a pair of jeans. Every article of clothing would then require an NFA stamp for the exact same reasoning that a car trunk or concrete tube did.
The intent of those objects is by design to be something other than a suppressor. The ATF looks at intent of the design. That is why the CAR-15 modulator is a suppressor, but a linear compensator is not.
More modern case in point, the use of an oil filter as a suppressor. IIRC the ATF now concludes the barrel mounting bushing as a suppressor. That is it's intent. The oil filter isn't - they aren't requiring the millions of oil filters made and sold every year to have a separate NFA stamp. But - affix it to the end of the muzzle, and the intent and purpose of the oil filter changes. it's not on a motor doing it's designed job. It's been repurposed for the intent of being a suppressor, which then falls under the '34 NFA.
You better then pay and have a stamp for it.
And that doesn't even scratch the surface of the speculative discussion of "constructive intent" in which an owner has parts in close proximity to make an NFA device. Pad the trunk of a car to put a sniper in it where sound is suppressed to commit a crime, I would think some prosecutors will be using it to work against the accused.
It may sound like we are now tilting toward thought crimes and exercising prior restraint. Hard to conceive some would go that far, but when your job is to protect the public, the motto lately is "Yes we can!"