I lived in all over Southern Ontario for 25 years, and saw only one external basement access, but that old house had no staircase to the basement. I've lived in Calgary for over 40 years. There are a dozen walk out basements at a golf course near here, and they are 50K$ less thatn the ones that don't have the walk out.
I know, go figure, right?
May well be from influence of the nearby American houses that are built like that.... Or even houses owned by Americans - we have a lot of that around the west coast.