-Europe is fragmented market. It is not given that German software will be gladly accepted and used in France, Italy or UK and vice versa. There are barriers there that does not exist in the US.
-The capital market and the stock market are not as developed as in USA in terms of market participants and available funds. Going public is unlikely event. If it happens, it would not get a lot of publicity and it would not raise as much money. Some European companies prefer to go public in the US.
-There is public mistrust about big software companies. Many people are afraid that big software companies will steal and abuse their personal data.
-There is also mistrust about venture capital and generally big finance institutions that they somehow "control" the economy, exploit small family businesses, and just make money on mistreating normal people.
I know that some of this sounds ridiculous, but it is true for astonishing number of people in Germany, France, Austria, and Italy. UK is a little better, but they mistrust everything about the rest of Europe.