EU membership had become such a divisive issue in Britain, he felt it had to be confronted properly.
As Cameron said in his 2013 speech: "Democratic consent for the EU in Britain is now wafer thin."
You don't answer the growing perception of a deficit of democracy with another commission of inquiry.
To put it mildly, the British have been reluctant Europeans - they made the initial decision to join on sheer economic grounds, not some sense of shared destiny or in being part of a peace project to prevent a Third World War.
Britain's political class forlornly hoped that incumbency would translate eventually to wider support.
Sure, if a referendum had been delayed another 10 years, a younger generation who have known nothing else but the EU (or perhaps hordes of immigrants and refugees) may have held sway and voted to stay.
But for Cameron the issue had urgency with the rise of UKIP.
Cameron wanted to cauterise the EU issue both from the 2015 general election campaign and as a destructive source of friction within his own Conservative Party. Those divisions have only widened in the course of the referendum.
But at the time, Cameron thought he could persuade the EU to offer Britain a great deal to stay in the EU, he thought he could persuade the public it was an irresistible deal, and he thought he would have an ally in Labour.
Not surprisingly , Europe didn't love its half-hearted partners across the channel enough to make an irresistible offer.
If the Remain camp had won, it would have been only by a small margin and that in itself would have led to continued agitation and destablilisation over EU membership. In that sense, even if Cameron had won, the issue would not have been settled as such.
With his re-election last year for a second term, Cameron had political capital to burn over the EU, which has done, ashes to ashes.
Europe's refugee crisis and the prospect of continued unregulated immigration from Europe added oxygen.
The fact that Britain cannot control its immigration from the EU is a legitimate concern which was not assuaged.
And the fact that Labour's Remain campaign was pathetic did not help garner support among its core constituency where Euroscepticism thrives.
Lessons for New Zealand? We need no lesson in how unedifying referendums can be. They can be nasty divisive exercises that bring out the worst in people and can end up being about anything. They should be used sparingly.
People's concerns about immigration and democracy should be properly addressed.
It is patently not in New Zealand's interests for Britain to leave the EU because the more friends and influence we have with it the better.
But "damage" to New Zealand will depend on the wider economic effects to vote will create and whether the fears over an exit have been over-estimated.