You have to invite a notoriously capricious and hair trigger federal agency into your life, sure less so than an automatic weapon but you still need to put yourself on their radar to some extent. After you've done that the first time $200 a pop isn't that big a deal but a lot of people are unwilling to take the initial plunge of putting their name on that list.
Harder than Europe though. Basically the same amount of effort as getting a machine gun. Full fingerprints, $200 tax, submit to ATF, wait months, then take possession.
And each state can have additional laws that differ from federal laws. CA bans ownership entirely I believe.
$200 tax is quite crazy though. You can get a cheap suppressor for that (or less). So the "tax" is literally doubling the actual price of a suppressor in the worst case.