This is pretty dangerous thinking. The EU only has half a billion people. Thus, the truth is: Over time, these companies will make infinitely more from developing nations outside of the EU than they would from the EU. especially if the EU is taxing them heavily.

Additionally, even if you say "don't care, if they leave we'll just build our own companies", now you are hamstringing the global growth of those companies.

(I'm just going to assume the companies that leave are not going to put your homegrown companies and people at a very serious technological disadvantage, which they might)

This is of course, why the EU wants everyone on the bus.