Because it's Ignatieff's fault that Canadians chose to give Stephen Harper a majority government that allows him to fill Supreme Court vacancies with his picks.
This sort of silliness is really uncalled for, in my opinion. Benefit of hindsight aside, it's more than a tad disingenuous to blame Ignatieff for what Canadians decided to do. Sure, indirectly Ignatieff could have offered a better alternative; no doubt about that. But this is like saying if only some less-psychotic dictator had taken over Weimer Germany, we could have stopped Hitler. It's absolutely true; kind of out of our control though, isn't it? (yes, I'm aware of Godwin's Law)
The reality is that this is the government Canadians wanted, and now they've got it. If anyone is to blame, it's the voters. They're the ones who voted for the guy, after all. Many people don't seem to realize this - voters gave us Harper because they wanted Harper, issues over 40% pluralities aside. Don't like it, don't live here. Democracy doesn't always end in the decisions you want, but it's the best we got.