You might think that, but that would basically defeat the point of a common market. Plus, the long game remains co-operation leading to convergence leading to political union (please). it might seem pragmatic to try to box and cox for a while, and perhaps it seems attractive to do so when the mood music across the continent is not towards integration but there will be a lot of resistance, quite rightly, to stepping back, even if you don’t currently move forwards.
There is an argument to say the EU would be better off without Britain (politically at least), but since I live in Britain, I’m not going to be saying that out in public.
In some respects it is worth remembering what the EU is.
There is the EC - this is the common market, same rules for doing business, free movement, no customs duties or similar, labour laws etc
There is the EU - this is the overarching entity which defines citizenship, includes the EC, but also has institutional involvement in stuff around justice, home affairs and foregin policy, purely on a best efforts, co-operative basis
There is the Eurozone - this is the bit with the common currency and all the monetary and lackof fiscal unity that entails.
Immigration aside, which is as I have argued before, taking up time utterly disproportionate to its actual effect on the country, as well as being a fig leaf for domestic policy failings, the political/economic stuff Brexiteers most commonly get stressed about it (a) getting pulled into the Eurozone and (b) the introduction of the EU leading to replacing co-operation on those non-EC issues with actual dominion over them. The irony of course is that no-one has suggested that the exception from the Eurozone, nor the limited involvement on justice or foregin affairs, should be altered.
It’s all fear for the future. Which is bollocks, because any such changes would trigger the need for a referendum under UK law, and even if the Tories hadn’t crowbarred that into our constitution, would precipitate a national debate on whether to pull out anyway.