The UK's attempt to join the (forerunner to the) EU was vetoed multiple times, by France. Your first sentence about how the EU "always wanted to have the UK on board" is factually and historically false. It never needed the UK to exist and it doesn't need it now.
As for "no hard feelings", tell that to your politicians, not us. Because they seem to think most so-called Europeans want the opposite.
Bon Chance!
48% of Brits, 62% of Scots don't feel that way.
And literally no one in the UK voted for what the government is currently doing or how shittily it is treating it's EU partner governments or EU guests living in the UK.
We'll be back, hopefully less arrogant the next time.
I think that's a fair description of how these things tend to work. Your only mistake is the assumption that because it's very silly nobody would actually use it, let alone that it wouldn't be incredibly widespread.
But as for the list, the EU came into being after WW2 so the USSR was out, Austria was politically irrelevant and Spain was a fascist dictatorship. Plus Turkey is on the other side of the Black Sea and the Greek really don't like them.
But the EU now already exists and the UK has been so insistent on having a special status that Europeans have gotten used to the idea of the UK not "really" being in it despite being just another European country like the rest of us.
It's okay.
You can leave.
We no longer need you for the EU to be able to exist.
We tried to accommodate you and make it work but we've understood that the feelings aren't mutual.
We'll still keep in touch with your extended family, though, and maybe over the next two years we can find a way that you can still come over to party sometimes, or y'know, just hang out if you feel like it.
No hard feelings.
Don't be a stranger.