Earlier quoted context omitted.
The reason the EU always wanted to have the UK on board had more to do with marketing than with necessity: Europe is France, England and Germany; if the EU was to be Europe, it needed those three in it or it isn't going to happen. It's also Spain and Portugal, Belgium and the Netherlands. The more the merrier. Open a history book and if a country playing a major role on the European continent is in it, it should prob…
"Played a major role in European history" is a very silly criterion. By those standards Russia, Austria, Spain, or even Turkey should be much higher on the list than Britain.
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.