its simply the cost of enforcement. The tax will help make sure the public is getting a cut, you cant just have a shell company on the backs of the american system without paying some locals. The tax will help fund enforcement efforts for better security, some of these "big" companies will be corrupt and there will be more money to help catch these bad actors. Also there probably has been some data done on how these shell companies run and with this one law you take out 90% of corruption.

There might be some good actors that get caught in this too and have to go out of business. If there is such thing as a good shell company???

You cant catch every drug dealer so you either focus on the big offenders and make them pay or you make drugs legal. I think its better for society if we do the former. Drugs are unhealthy.