North America uses TERPS and pretty well everybody else uses PANS OPS. Canada (and I think Mexico) piggy back along with these essentially American rules because that's just what we do with just about everything
The Americans are just wanting to keep things the same and not take a back seat to anybody else for any reason. Most are shocked to find that there are places in the world that don't use inches of mercury for altimeter settings, and have transition altitudes lower than 18000' because that would just be silly.
I admit that I was once of this mindframe as well (Canadians don't get out much either sometimes) but having seen the advantages to PANS OPS approaches, etc. I now consider myself a convert.