First, who appointed these guys leading contenders for the leadership of the Liberal party? Did they answer a job advertisement? So far as I know, the Liberal Party has not even determined when it will hold a leadership convention. The whole idea, then, that these are leading contenders is at the least, a bit pre-mature; at worst, misreporting. No one knows who is a leading contender. It illustrates the arrogance of Canadian journalism, however, that someone who works for The Globe feels they can just annoint a leading contender in the absence of any evidence whatsoever, in the absence of a leadership selection process, in the absence of a date on which a leader will be selected, in the absence of any consideration whatsoever as to what the issues involved in leading the Liberals might be. Or, in the absence of any discussion of what these different men stand for. Process, facts (as in dates), and issues don't seem to count for very much.
Second, what unites these three men -- Tobin, Manley, and McKenna -- is that they are known quantities. Journalists working for the Globe know who they are. There is a certain name brand recognition to them and, if you were just trying to compile sort of list of people who might run, well, these guys names might put up. Who else's name might pop up? Well, there are other names but these guys are the ones who would be there and so not much thought is required to put them down as potential leadership candidates. It can be done without any consideration for issues (its not clear, for example, exactly what issues are near and dear to Mr. Tobin's heart, its not clear where he stands on child care or tax cuts, etc.) or what issues Canadians might find important. For journalists who are decided un-used to talking about (or, reporting on) such things as issues, these candidates have an appeal, then, because you can talk about them without having to talk about issues.
Finally, they are all yesterday's men. And, this is the real reason I suspect we are hearing about them. You can write a story about McKenna or Tobin or Manley without having to actually reseach the story. Anyone with a reasonably accurate memory can pen a brief story about McKenna, Tobin or Manley. None are particularly ideological (Tobin, for example, is more of a rah-rah nationalists than anything else) whose best days are behind them. Consider other potential candidates would require some actual work before the story was put down. For instance, reporting on Martin Cochon, for English-language journalists, might be tough because he is not a known quantity. One would have to call people, read his speakers. The same point can be made for Stephane Dion. We know he was a minister but what does he stand for? Well, the simple fact is that -- like it or no -- he does stand for things so writing about him as a leaership candidate is hard. More research, more interviews, more reading, consideration of tough issues. And, the same thing could be said about Michael Ignatieff.
Why do I mention this bunch -- Cochon, Ignatieff and Dion -- because these are the real contenders (not McKenna, et al). And, all these candidates will stand for something. They don't make an easy story. As a result, the Globe ignores them in favour of three guys about whom you can write a story without having to consider anything new. The real story, then, is not that McKenna et al did not run for the leadership. The real story is that the real story was missed becasue Canadian journalism is so bad.