But the US can't just block offshore companies from its market without absolutely destroying its economy.
What do you think would happen if the US suddenly decided that no company can do business in the US without paying taxes to the US for their offshore profits?
You only have to injunct one. After a couple million in losses, they'll pay up. At that point, the threat of injunction would simply get the other ones to pay.
Or, you start seizing domestic property to pay taxes on the foreign assets.
Do NOT assume the government is ever powerless. It is always bigger than you.
What do you think would happen if the US suddenly decided that no company can do business in the US without paying taxes to the US for their offshore profits?