Because the scared punter is an easily manipulated punter.
It's funny you should say that, BradfordLass, because when you start looking at the reasons that Leavers give for their vote they are most of them based on the emotion of fear. Pumped up beautifully by most of the media and by the Leave campaigners who were short on detail but long on fear.
Leave voters were scared of losing sovereignty, scared of being forced into a federal state of Europe, scared of their children and grandchildren being conscripted into an EU army, scared of being swamped by 3 million Turks who were just about to join the EU and invade the UK en masse; to name a few.
On the other hand, the Leave campaigns were very careful not to scare them further with the facts about how very difficult it would be to leave an institution with which we had been intimately involved for over 40 years. Nothing scary about that, of course. We'd never leave without a deal, the EU would be begging for a trade deal with us, we'd make trade deals all over the world at the drop of a hat, our seas would be full of fish again and we would lord it over those pesky Europeans who tried to steal them from us.
So now Leavers are fully primed with the most unrealistic ideas about how we were going to find it so easy to break with the EU and are frustrated because it is taking much longer than their trusted gurus said it would.
It isn't the Remainers or the EU they should be blaming for their frustration; it's the lying buggers who promised them the undeliverable. The ones who are now in power and who are blasting holes in our constitution, parliamentary democracy and economy in order to satisfy the monster they've created (and a number of them expect to make a lot of money for themselves out of the ruins).
The most sensible Leaver I know of had a Plan. A pretty workable Plan. It would have taken about 10 years to implement it but it would have been reasonably painless and not divided the country. But sense has never been a feature of the last few years...