Suppressors got wrapped in with the original 1920s (ish) "machine gun" ban when old timey mobsters were rampant.
At least that is my understanding of the origins of the "why."
By way of clarification:
The 'ban' was actually a requirement to register such devices (machine guns, short barrel rifles and shotguns, 'any other weapons' (AOWs) and suppressors) with the feds and pay an exorbitant (at the time) $200 tax, with insanely high penalties (10yrs/$10k) for non-compliance.
That law was the "National Firearms Act of 1934" (The NFA), the first of many federal transgressions against an uninfringed right to keep and bear arms. Prior to becoming law that one could not possess such items like free men, it was challenged in court in a case that lost by default, because the accused (a backwoodsy sort that didn't know (likely) or didn't care) failed to attend.
The second major transgression was the "Gun Control Act of 1968" (GCA'68), in which one could no longer buy new firearms direct, no longer commercially sell firearms unless a licensed dealer (killing the "Western Auto" and other hardware store brands) and all dealer sales were recorded (hello Form 4473). The NRA backed this law.
The "Gun Owners Protection Act" (GOPA 1986) purportedly allowed lawful gun owners to safely transport their firearms through unfriendly states (NY, MA...). It was attached with a rider at the last minute barring possession by and transfer to regular civilian citizens of machine guns manufactured after 1986, hence the "transferable " status (and inflated value) of MGs made before '86. In 1985, a Colt M-16 was the same price as a Colt AR-15, today...what? $20k or more, while decent ARs can be had for a grand.
Been downhill after that...
The suppressor/silencer regulation is one of the most far fetched and dumbest sides of federal law. Everywhere else in the world it is considered bad manners to shoot without a silencer. Regulate an inert device with no innate ability to do anything, and regulate it far more than a Title II firearm like a regular long gun or handgun. Harder for most people to get, and afford, than a pistol that actually shoots bullets. I guess they were on a roll...
You can't legislate reality to your liking. The technically, scientifically correct term is suppressor. Silencer is the slang term.
While I'd agree that "suppressor" IS the technically correct term IF describing function, "silencer" is NOT slang, it is the long term legitimate name for the device, however scientifically inaccurate.
The inventor, Hiram Maxim, called it a "silencer" in 1902. The BATFE calls it a "silencer". The law (18 USC & 26 USC) calls it a "silencer". My Forms 4 calls them "silencers". No one is legislating reality. Either term is acceptable.