A senior Labour politician at the time was asked why the remain camp didn't make a better case for staying in and he replied because for most people it couldn't
It is indeed hard to explain to people the benefits of EU membership when the vast majority of the public were and still are blissfully unaware of them.
Ive yet to have a discussion with a brexiter who has any understanding of how the Single Market works.
The common rulebook is misunderstood and is commonly called "EU bureaucracy"
What the EU have done is take national standards, industry standards and written them into a standard format so they are harmonised.....thats a lot of work and in that sense the EU are bureaucratic.
BUT, once those standards are all common to the 28 countries...each business can trade freely without trade barriers.
It enable small and medium businesses and consumers to buy and sell throughout EU with no trade barriers
In simple terms the Single Market front loads the bureaucracy so businesses can sell and buy with no barriers
And the reason why a politician cant make a case for it: because its technical, its complicated, its boring and so not easy to sell as a political slogan.
however "get back control" "get back sovereignty" etc etc is easy to sell.....even though it is meaningless and falls apart under scrutiny and is demonstrably untrue