For Britain to leave the European Union, it would have to invoke Article 50 of its treaty, which would trigger exit negotiations. Only the U.K. can do this—it can’t be invoked by the EU—but it doesn’t look like it’s going to happen any time soon.
Cameron has said he will not invoke Article 50 as prime minister. That pushes exit negotiations, at the earliest, to the fall, since Cameron has said that he does not plan to leave office for several months. While the delay could prolong the period of uncertainty and instability that Britain finds itself in, there are practical reasons to wait. It gives markets time to stabilize. It gives Britain time to figure out what exactly it wants from the EU during exit negotiations. For those on the Remain side, it also gives the country time to consider what exactly it has done and, perhaps, creates the conditions for a re-vote.
Cameron’s reputation has been utterly obliterated, but he has nothing to lose by playing a game of chicken with his likely successor, the buffoonish Shakespeare scholar Boris Johnson. By waiting to invoke Article 50, he’s forcing responsibility for the Brexit onto him.