I wonder if it's just a Canada / US immigration thing? Even then I find it a bit hit and miss.
I don't recall encountering any problems with immigration in Asia and Europe either.
While I skip the regular line nowadays with Nexus, I do recall a lot of questions coming back to Canada in the past. I was complaining to my friend who works in customs (and YVR specifically in the past) about getting the third degree waiting for my luggage at the carousel and IIRC, his answer was that part of it is to get you somewhat uncomfortable and see how you react.
On the flip side, even with Nexus, I feel I get grilled by US pre-clearance at YVR lol