The EU was possible when times were good with richer countries shelling out money for poorer ones.
But the GFC caused many EU members economies to collapse (Greece, Portugal and Ireland). With one currency the Euro it was like all the countries economies were chained together and when some started sinking they took others down with them.
I'm all for EU countries standing together but its important to remember that their independent nations with different economies and people.
This is the Game of Thrones
Where you either win
or you DIE