US companies are free to not operate in Europe.
There's nothing special about US software engineering vs. software engineering made elsewhere from a purely technical and know-how point of view.
The key difference is availability of capital and appetite for risk that make US exceptional by enabling a speed of scaling and execution not possible anywhere else (well, other than China).
If US companies that can't be bothered to follow EU laws leave the +500M people market that is the EU, I'm positive some other equally competent alternative (local or otherwise) would appear sooner or later to fill in the gap.