There is nothing hindering European startups to raise money from all over Europe. Except that Europeans hate to invest in real businesses and love investing in real estate.
American startups and businesses get investor money from all over the world, including from Europe. Willingness to invest in startups depends on the downstream of willingness to invest in business in general. If venture capital investors know that there's a lot of money willing to invest after the startup phase, then they are willing to take more risks. And so on for every phase of investors, until you reach big institutional investors like retirement funds.
It looks like the proponents here have fallen into the classic European thinking: "Let's talk and make papers to make our wishes become true". Instead of trying to understand reality and why things are the way they are.
They should ask themselves why any European investor would want to invest in a European startup instead of in an American startup. They should ask themselves why European entrepreneurs should create their startup in Europe instead of in America. When they have the answers to those questions they know what solutions to propose.
My experience doing business in and with America has been nothing but fantastic. They have all the infrastructure and all the culture to help entrepreneurs and anybody who wants to do business. They want to do business as well. Need a credit card processor? Need an LLC? Need a bank account? Need a business loan? It's easy, the USA is fucking open for business.
In Europe it is hostility mostly all the way, from banks to regulators to governments, and so on. The easy part is registering a company, which is just as swift in Europe as it is in the USA. But apart from that you won't find any friends in the process. Even if you're European. Even in the country and the city you were born in.
Americans love new things and new ideas and see them as opportunities. Europeans see them as threats. And that is mirrored everywhere you turn. You might agree with the European perspective in a society-wide perspective, but for startup businesses the American mindset fits much better.