While the EU has a very well integrated market for industry goods, for services (where I would include software) the market is less than perfect.
The language barrier is the biggest strangle for EU software entrepreneurship / platform business in my opinion.
The second-biggest obstacle imho is funding. If you want to grow really fast, it is hard to get enough money.
Third, I would rank ecosystem in general, besides money.
I think over regulation is not as bad as it is often said. All developed countries have regulations in place, some more some less.