Canada

They are things like having different requirements of a "first aid kit" in each province,

There are quite a number of different regulations for commercial vehicle equipment and operation across the provinces.

BC has some rules that were created to address thwir mountainous roads. Ontario has some of the most extensive rules on what the vehicle must be equipped with. The rules surrounding tire chains and studded tires differ across the country.

Of course, ir should be possible to harmonize them all, but that would put added burden on operators in some regions where certain requirements don't make practical sense.

(Why would a truck in PEI need the same safety equipment as one operating in the BC mountains?)