They wanted the country to be able to spend its own money, manage its own borders and pass its own laws. You can't do that in the EU and you can't do that with a 'soft' (fake) Brexit.
To suggest that they must understand the mechanics and minutiae of trading protocol and arrangements before they can ask for that is bit orf, tbf. We have a large political class and civil service who are paid to grapple with the details, and the fact that this class is claiming that independence is a technical impossibility shows the true technocratic, democracy-phobic soul at the heart of the EU.