Where to begin with this.  Sigh.  Point one:  In my riding we don't vote for a Parliament or a PM - we vote for an individual MP.  Point two: the reason people rank their ballots to lean to the centre is...wait for it...the centre is where the majority of Canadians live politically.  They don't want extremes of the left or the right calling the shots, an example of which we are currently seeing in BC.