Funny pics
but nevertheless there are many other countries in the past that should not have joined the EU!
Just from the point of view of core EU members:
Expanding the borders does not just make it easier for manufacturers to move labour into cheaper (once upon a time) eastern block countries and thus limit the work available for their own workforce but also the funding by the EU that has in the past and still does go to needy places like Cornwall, UK or the eastern part of Germany will be pretty much limited.
There are newcomer exeptions of course that do fit in really well