My guess, is that Ontario voters don't trust anyone but the Liberals to keep Canada together. Ontario views Ontario as of the essence of Canada, and the Conservatives all about the estranged plains.
(Denny Crane: "I Don't Want To Socialize With A Pinko Liberal Democrat Commie.Say What You Like About Republicans. We Stick To Our Convictions. Even When We Know We're Dead Wrong.")
Ontario has been running the country since Confederation.
I don't know why people are so surprised.
Just to add to your comments, many people see the Liberal party as holding true Canadian values and the Tories don't. That's what makes me sad about my homeland. Everyone is brainwashed into thinking that the Liberanos repesent all of Canada and no other party comes close.