We make B2B software that we sell in several EU countries, which interfaces with official systems. Even though all countries are subject to the same EU rules, and follow the same underlying technical model, each country has its own laws and regulations, and separate implementations. So even though our software does "the same thing" in each country, it's so different that a lot of code is per-country, over 50%. So it'…
Easy, yes, but expensive for the business and its customers. It's a silly way to do things, but it's hard to see an alternative without member states giving up massive amounts of sovereignty.