I think one of the largest things holding back startups in europe is the fact that there still isn´t one Europe. You still can´t offer your service to all 400.000.000 people from one office, rules are different across borders, languages, etc.
If you have a service you expect 1 in a million people to use, you can have a userbase of 300 in the US, but to get the same number of users in Europe you will need multiple translations, manuals in multiple languages, knowledge of the regulations in multiple countries, etc. Even if on paper Europe is a larger and richer market.
If you have a service you expect 1 in a million people to use, you can have a userbase of 300 in the US, but to get the same number of users in Europe you will need multiple translations, manuals in multiple languages, knowledge of the regulations in multiple countries, etc. Even if on paper Europe is a larger and richer market.