I am the poster of this topic.
After reading replies, I am baffled that why are suppressors/silencers do hard to get when they can protect irreparable damage done to ears by guns?
The National Firearms Act of 1934 established high taxes and laws regarding transfer of certain weapons and accessories, including silencers. It was an attempt to reduce the availability of things like machine guns and silencers to organized crime, back during the original gangster era in the 20s and 30s.
Don't look for it to get repealed any time soon.