Because in 160 areas, people chose to pick the conservatives over the others.
I'm sorry to bring this up again, but I actually ran the on this for another forum after the last Canadian election.
Data from here.Of 308 seats, 145 were won with an outright majority (>50%) of the votes. That's roughly 47%, with 53% won with only a plurality.
The Conservatives actually did better than average, holding an outright majority in a full 107 seats of their 160 seat total. But that's still far from them having clear majority support in a majority of wards.
Lowering the threshold, 42 seats were won with less than 40% of the vote (11 Conservative) while two were held with less than a third (Vancouver Centre by the Liberals and Ahuntsic by BQ).
These numbers are pretty good comparatively. In the 2010 UK elections, out of 650 seats, 432 were won with less than 50% of the vote. That's a full two thirds of Parliament, almost exactly. 110 (17%) were won with less than 40% and 10 seats were won with less than a third of votes behind them.
That's why I'm not a fan of FPTP. You can (and commonly do) have well under 50% of the voting public supporting the winning candidate. Even if you agree that you need a single representative for a given population, a representative elected under FPTP was likely dependent on only a minority of that population's support.
Under AV (or IRV; lots of different names for the same thing) a candidate needs at least the consent of 50% + 1 of the voters. They don't have to be their first choice, just ranked above other candidates. AV isn't necessarily more proportional on the national level, but it means the elected individual is more representative and answerable to their constituency.
For Westminster style parliaments it simply makes more sense.
And yes I'm still sore about that referendum.