You can't really require studded tires in a place that can have 2 weeks of lots of snow, followed by 3 weeks of no snow and repeat.

You'd have to repave the entire city each year. And you can't expect motorists to keep adding and removing the studs as the weather changes.

Studded tires are only realistic in a place where you need them for an entire season.

Snow tires on the other hand can help a TON. But not everyone has room to store them in the off season.