> Why doesn’t every country mandate daytime running lights like Canada has for decades?

Not everyone drives an up-to-date vehicle and TBH, some vehicle owners do not care that they are a hazard, regardless of what the law requires. Here in Austin, when the police get in a snit, they just stop enforcing the law and even when they're not in a snit about something, there are parts of town where traffic laws are traffic suggestions. All of this makes for a somewhat hazardous driving environment at times.