I lead a payments team.
US requirements around what we put on invoices: 0 EU requirements around what we put on invoices: Still figuring it out
The technical implementation is not difficult. It's dealing with all the lawyers and accountants who have to understand regulations of 27 different countries.
There is a significant difference between "not regulated" and "regulated at all". The burden of understanding the regulation itself is a cost, even if the actual compliance turns out to be simple.
I'd also like people to name specific regulations they disagree with, yet any time I challenge s/o they slink away.
In this case, a stripe rep in this thread posted a list of their todos for the EU. Note that literally "putting VAT ID numbers on invoices" makes their top 5! Can't be that bad after all:
"localize the invoices, add EU specific payment methods to invoices, improve tax support, make default invoice templates EU compliant with VAT ID"