This list will give you an idea of what Stephane Dion was up against as he faced his caucus the day after the election. Also, you might notice that some of the pretenders that are "thinking of running" all supported a certain frontrunner. This is called "scaring the potential others" out of the leadership race (Coderre, Dhalla, McGuinty).
So, guys like McKenna and Manley look at lists like this and realize they start waaaaay behind the 8 ball and decide not to run. And, even if Stephane decided to fight a review and Gerard's guys backed him, it would be a knife fight in a dark alley. The only name I see as not a pretender right now is Domenic Leblanc. He was neutral last time, is young, bilingual and has deeeeeep connections in the corporate world.
Scott Andrews (citation needed)
Shawn Murphy (Via Brison)
Anita Neville (Via Dryden)
Massimo Pacetti (Via Volpe)
Michael Savage (via Brison)
Judy Sgro (via Martha Hall Findlay)
Kirsty Duncan (Citation needed)
Mark Eyking (VIA Brison)
Martha Hall Findlay