This first one seems the largest hurdle w.r.t. startups. If you are a startup founder of say a ride hailing app - the total addressable market is much larger in the US for the same level of effort. If you want to scale beyond your home state (i.e. California) in the US, there are probably just a handful of different state/city taxes/regulations that need to be accounted for.
If you start in a country in Europe, you need to factor in:
- language translation of the entire app
- different country cultures/customs (i.e. tipping, wording of prompts and promotions) - even down to the naming of the app which might have a negative connotation in a different language
- prior to the Euro - differences with respect to currency, trademarks, patents, etc.
- entirely new country regulations and politicians that need to be "handled" - each in their own separate language which means a separate lawyer and lobbyist needs to be on staff for each country
- home court advantage - French probably prefer to support LeCab while Spaniards probably prefer to support Cabify