Which companies would that be?
I can imagine what would happen to Google if, through some dark miracle, their leadership decided to do this.
Most of their top engineers live in America. So do the leaders, but ignore them, we've already decided they want this. The employees don't, though: There are eleven thousand people, there, who'll need to be relocated to - where? Europe, probably Ireland, where many of them have never been.
Certainly not where they have roots, or where their family is.
Google has deep pockets. They can afford to pay massive relocation bonuses, and they'll have to do so. Still, this is eleven thousand people; we're probably talking about a billion plus, just to get a reasonable number of them to follow. After all, most of these engineers would be perfectly capable of finding work at a different company.
Okay, so they've done that. They lost a lot of good people; probably a lot of their best people, the ones that care least about money. Still, they're now in Europe.
Now what?
Most of their infrastructure is still in the US. Compute clusters, god only knows how many. Storage clusters. User data, placed in the US under safe harbor provisions because an attempt at keeping it in Europe is unfeasible given the rather diverse tapestry of privacy laws here.
They'll need to move it all to Europe. They'll need to figure out a place to put it, and they'll need to pay billions - quite a few - to rebuild and expand their infrastructure here.
By the time this is all done, they'll have new problems. Realistically, they'll go bankrupt somewhere in the middle. And that's not mentioning possible reactions from the US government.
It would be great if leaving the US was an option, but it really.. just isn't.