Countries are basically politics and economy.
Each one of those countries in the EU have different ones.
That's partly why the EU is so complicated, it has to work with many different political and economic frameworks. Some countries in the EU don't have the Euro for example (that's the Eurozone) such as Denmark, and Sweden for example, whereas others are not part of the EU but still are pretty much involved in many things, such as Norway. And so on, it's a complicated thing.