If one really wants to know WHY suppressors are so expensive in the US.
The answer is easy, start your own suppressor business, get a local /state business license and the corresponding tax / employer numbers, the type 7 FFL ($150.00 3 years), first then apply for a FEIN (Federal Employer Identification Number), then the S.O.T ($1000 + USD annually based /due on the month of july). This is even IF there is NO employees and is privately owned. This doesn't include the excise taxes, and the IRS higher taxation of being self employed.
Now for the hard part compliance which will cost either in manpower, or software, and last but not least research for new rules. Honestly that is what drives the price up and well as the materials cost, labor, tooling cost, etc.