Look at how quickly Cameron resigned after the vote. He wasn’t truly interested in finding a good deal, he was relying on the fact that people would vote remain regardless. I’m guessing due to the remain result in the Scottish independence referendum not long before.
Indeed - and in my opinion he'd completely misinterpreted that as a great success rather than what it was, a very narrow victory that burned a lot of political capital.
Or he resigned because he believed the leave decision could better be implemented by a leave campaigner, who would approach the matter more earnestly and enthusiastically.
Or more specifically, leave EU is a political and economic disaster and mess he wanted to not take part in. Even if you succeed you will be covered in dirt.
Just look at May now and imagine Cameron in her shoes. No politician wants this.
Allowing the referendum was an interesting but silly motion already, a gross miscalculation.
He came out of that looking the fool and if anything actually helped the leave campaign.