Long story short? It’s protectionism but there’s a reason for it.
Here in the US we overproduce milk because it’s subsidized. We REALLY overproduce milk. It’s to the point where farmers were dumping the excess because they simply had too much so the government came up with a solution.
“Government Cheese”. A pasteurized cheese product that kills two birds with one stone. Our dairy famers continue to overproduce milk and the excess gets turned into processed cheese food product. Yummy,
We still have too much milk so we look to ways to unload it and Canada is a good place for it. Problem is they don’t subsidize their dairy famers so milk prices up there represent the actual price of milk. If they allowed our dairy up there it would destroy their own dairy industry so they place huge tariffs on it. And then there’s the fact that our milk is so full of hormones and stuff that Canadians don’t want it.
Now down to New Zealand. They don’t overproduce milk but due to their climate their cows can produce it year long leading to them being a dairy exporter. They see Canada’s protection of their dairy industry as unfair.
But here’s the problem. If Canada allows New Zealand dairy to show up their shelves that opens a door for our dairy to show up there as well and again that would kill their dairy industry.
So the protection stays and New Zealand can’t sell their milk in Canada.
EDIT: I don’t freaking know the ins and outs of global commerce, trade or anything else. I’m going by what I’ve managed to read on the subject yet people are asking questions I have no answers to because I’m not an economist.