The problem in Europe for start ups is rarely the supply side, it's the buy side; large EU companies don't buy start ups at the rate that large US companies do. This restricts the volume of exits, and therefore restricts the available funding; organisations that fund VCs normally get their money back in 5 to 10 years, but with less exits that means that VCs don't raise as often (which over averages means collectively they don't raise as much) because they don't get back as often.