Anora was way to harsh and unforgiving. She will not earn the loyalty or respect of her people alone.
Cailan was a moron, and while he would be loved. He would make political blunder after blunder.
Logaihn was so racist and traditionalist that he would see his country die before he seen change.
These particular qualities are all extra crippling for a leader to not posses. I kind of liked how the Dev's showed this.
Anora and Cailan were probably the most effective working together. All it would take though is just one of them dieing and the system falls apart.
Like I said they all lacked a fundamental quality necessary for a truly inspiring and good leader. Sure you can call it human, but I call shenanigans.

Fair points, I agree neither Loghain nor Cailan were capable enough to lead Ferelden on their own. But Anora, while admittedly being somewhat heart-less at times, would have made a decent Queen on her own. She wouldn't have captured the hearts of the people, but would have had enough political know-how that she wouldn't necessarily need it.
I should point out that I haven't played the game properly in a little while so if I'm missing a big piece of evidence then please point it out.
