Normally, in a parliamentary system, when the government loses a vote of confidence in parliament, the government resigns and a new election is held.

This referendum was more or less a confidence vote on the government. If British democracy were functioning properly, the government would have resigned, and the people would have had a chance to elect pro-brexit representatives.

But Britain adopted fixed election dates, copying the American electoral system. And referendums, for that matter, aren't very parliamentary.