Nope, bulgaria is less strict, i know lot of people here with USA LLC, without issues with the tax administration for example - they not treat it like a local business, like what the france, spain and germany can probably do
There are some possible explanations for this:
1. Bulgaria has actively decided not to enforce their own laws, in exchange for people spending time there and spending money (same as e.g. Portugal, Thailand, maybe Cyprus)
2. They don't have the resources to properly investigate this, so they go after the big fish, not some small freelancer making 4k a month
But I can guarantee you, they haven't actually written into their tax code that "register a US LLC, run it from Bulgaria and we won't tax it" - 100%.
You will see that if you're a Bulgarian citizen making $$$ with a US LLC, they will tax it.