David Cameron famously got precious little from his pre-referendum attempts to negotiate a special position for the UK in relation to existing EU treaty obligations. This was despite almost certainly having held many more cards back then than UK negotiators will do when Article 50 is eventually invoked. In particular, he was still able to threaten that he would lead the Out campaign if he did not get what he wanted, whereas now that the vote to leave has happened that argument has been entirely neutralised.
In the end, the decision for the UK to formally withdraw its membership of the European Union passed with a reasonably comfortable majority in excess of 1¼ million votes. Every one of the 17.4 million people who voted Leave would have had their own reason for wanting to break with the status quo. However, not one of them had any idea as to what they were voting for next. It is one of the idiosyncrasies of an all-or-nothing referendum.