> Once it got to the hard work of making it happen they realized how awful the deal would be and how the economy would be harmed. Because they didn't want their name attached to it they resigned.

One could argue that they didn't expect the vote to pass at all, and did it to gain favor with their constituency - to be able to say they "tried to leave the EU but alas." They knew their promises were untenable, yet they made them anyway, but there's no way to fulfill them once the vote passes, hence resignation.