Hey Married a Canuck.
Sure there's nothing wrong with a share of through traffic, but as a sovereign nation, each would not want too much of their own traffic flowing through other carriers. It just robs you of your own potential.
I think a main diff here is that AC does it through an alliance seemingly sharing the poker pot, where our own Emirates seems to not want to go this route. This I believe is what nations are sitting up and taking notice now.
Sure Singapore flies to Seattle now, but rest assured, there is reciprocation. Cabotage is still illegal in the USA, and for the very reasons being discussed.