I lived in the UK for a decade until Brexit.

Most of the population has massive Nationalistic Delusions Of Grandeur, including Remainers (one of the Remain arguments was "We should stay in the EU and change it from the inside" or in other words, Britain and it's 50 million people know best and should be making the other 470 million and 27 countries to change their community for the benefit of Britain), though the Leave campaign was incredibly deluded, mainly anchored on what can be summarized as "we'll leave and they'll still give us the priviledges of membership but without the obligations".

There really was none of the "let's cooperate for the common good" spirit that most other countries have (some more of it, some less) with regards to EU membership, and their take on the EU was all "what can we get from it" and, as far as I can tell, still is. (This, by the way, is quite consistent with how Britain behave when inside the EU: it was allways "what's in it for me", always a you win or you lose vision, seldom if at all win-win)

Until that widespread heavilly nationalist and quite deluded spirit amongst the British population changes (and all that stuff is heavilly pushed by the local Press, with for example the coverage of International news there always slanted to make it seem like other countries are listenning to Britain and its PM, which is very much not the idea that the coverage of the same news in other countries passes) Britain won't be back, and frankly, having seen it up close and personal from the inside, I think is best for the rest of the EU that Britain stays out until its people accept it's just another mid-sized country and Britain becomes a normal country rather than this "old wierd uncle of Europe who is constantly going on and on about war stories which are almost a century old"