personally I think it's a combination of the illegality of it barely being enforced in the first place for users, and all the available political focus and capital being completely taken up by other matters - the immigration/refugee crisis and rise of right-wing populism across the continent for example (right wingers being exactly the kind of people to impose "law and order:, and not be too favourable to progressive drug policies) among other things. brexit in the UK, catalonia here in Spain, the reactionary regimes of hungary and poland. the nordics - who would otherwise likely be the policy leaders in the field, given nordic social democracy - are I believe notoriously strict on drug laws and culture, and I'm not sure why? etc etc
meanwhile in the US devolved state legislation means different governments and parts of the country can all proceed at their own pace even if President Wacko would never legalise, and of course that means progressive areas like colorado and the pacific northwest push right on ahead. Canada under Trudeau has so far avoided the whole right wing populism thing (though who knows for how long given current trajectories) and, besides I guess the China and Saudi Arabia diplomatic crises and that whole domestic legal fiasco, maybe had their political landscape free enough for this sort of thing to go through?
basically I imagine it's like how germany took forever to legalise gay marriage, mostly because of political inertia and other priorities, without really reflecting the changes in the populace.
