... for good reason.
Is there evidence to show that the BBC and CBC have reduced polarization in Britain and Canada? One could argue that they have plenty of their own biases and are not especially good at detecting or correcting for those.
They aren't on the same level as major US news networks when it comes to distortion and agenda-pushing though. This is my opinion, but there are plenty of systematic studies that show the same thing. If you look but can't find any then I'll come back with links.
The only reason for why there isn't a CBC equivalent in the US is 'because it happened that way'. Trying to find some generalized reason in this particular artifact of a political culture is like trying to find reason in a drunkard's walk.