Why? Because, although Britain is likely to stay in the EU, Brexit will remain a live issue unless the eurozone can sort itself out. That means either admitting that the euro has been a terrible mistake, or going the whole hog and integrating further, with a single banking system, a Europe-wide treasury, and a democratically elected finance minister with the power to raise money in Germany and spend it in Greece.
That is actually the problem. To make the euro, the eurozone, work it will be necessary to do what no one will actually do.