Fascinating. I've never flown in to or out of Mexico, nor traveled beyond the border zone on a land crossing, so I had no idea. I find these special immigration situations to be very interesting.

I knew for a long time that for a land crossing from the US to Mexico, there was no entry control, but you officially needed to get a "tourist card" to travel beyond a certain distance, but had no idea how strictly this was enforced, if at all, for US citizens.

Only fairly recently did it come to my attention that there was an admission status to the US that allows certain Mexican citizens to enter the US across a land border, but they have very limited lengths of stay, and cannot travel past a certain distance from the border. There's certainly no such limited admission status for Canadians, or other nationals arriving at an airport port of entry.