If I build something in California, to California's laws, and it becomes a success, I can immediately sell it across the entire rest of the US, and I can expand across the US, using the same employment contracts as in california, same lawyers as in california, etc.
Sure, later on I can save money by making the Delaware version of my product with more cancerous chemicals, or have stricter NDAs in my Florida contracts.
But if I start with California regulations, I can expand to the entire US with a small team of employees.
There's nothing like that in Europe. If my product works in Germany, I'll need a french, spanish, italian translation to sell it in these countries. I can't just hire people from these countries either — they've got different holidays, different work hours, different unions I'll have to deal with. Different tax codes and agencies. And often these are conflicting with one another.
In the US, I need one or two support shifts in one or two languages. In the EU I need 27. In the US, I need one version of the product, with one plug. In the EU, unless I'm okay with 10A and a plastic chassis, I need a dozen different versions.
And even if the product can be used universally, European culture is significantly more diverse than US culture.
Is a phone call at 7am or 8pm more appropriate? Depends on whether you're in Germany or Spain. When a job applicant includes a photo of themselves and lists their parents' degrees and jobs on their own CV, is that appropriate or not? In Germany, that's often expected, in many other regions, a huge no-go.
To be successful in the US, I need to build one company. To be successful in the EU, I need to build a multinational corporation with 27 local branches.