It’s not simply the fact that they wilfully misled the people but the fact that they so horribly misread the international situation, and continue to do so. The narrative persists that everything will be okay once the international situation returns to the balance of 2015. It won’t and it never will: Russia is set for the long game in Ukraine, China is not posturing and can turn the screw, and India will have its pound of flesh.
If anything, the international situation is going to develop in ways that make Brexit successes even more unlikely.