There is no logical reason for Porte being unable to win but I just struggle to imagine it happening. Too much time as a domestique? Echoes of his pug faced predecesor? Too nice?
Every year he does well in some early races, people say he's in for a shot of winning something big, then he seems to just hover in the top 10 for the TdF and the like.
Porte never seems to have that hunger to win. Both Porte and Froome always comes across as friendly and genuine media wise (to me at least) but Froome is always 100% focussed on getting what he wants.
Agree with @croft - Porte for the win this year as long as he doesn't get hit by a motorcycle or a dog.