I wanted to ask why Canada isn't exercising its right. You have some ideas, but we can only speculate. We don't have the answer.
Let's look at the Quebec City airport, for example. One of the concerns raised is that, for the Montreal and Toronto airports, part of the costs were recovered as a result of different agreements with the government. The new agreement says that airports that choose to set up pre-clearance—this also includes stations—will cover the related costs.
Let's take the example of an American airport in Arizona or Florida. Perhaps the airports don't want the system because they find it too expensive and they don't see the benefit?