Good luck selling software across the EU if you live there. Check out the new VAT rules the EU imposed. It's less paperwork to sell to everywhere but the EU, which is madness.
With VAT, you have to keep careful track of input VAT and sometimes later claim repayment from various governments.
There is a lot of obligatory registration and document submission.
The velocity of legislative change is high, especially when summed across member states.
Small entities have an incentive to underreport. Thus, a lot of enforcement activity is targeted at small entities.