I think it is sadly a result of influence of their lucky and wealthy neighbour Alberta and trying to replicate that success using misguided cargo cult methods.
Alberta of course massively wealthy due to the fortunes springing up out of the ground, and over the years has been able to draw Canadians from all sorts of places at times where their own home province was relatively economically depressed.
Alberta also has a conservative political culture and some unique ideas around how to organize things that were particularly different from, as you said, the "let's work together" approach of Sask under visionary leader Tommy Douglas and those that followed that social democratic road map.
So I think you had a combination of Sask folks going to Alberta to work in the oil sands and picking up the politics and coming back with it, and the centralized conservative media touting Albertan success across the border as a road map for Saskachewan success.
Of course the reality is that Alberta's success likely has a lot a lot less to do with their political policy choices, and a hell of a lot more to do with the fact that they get absolutely ginormous oil royalties that funds their every budget wish.
Saskachewan trying to replicate what Alberta has via the policy side, without the resource royalty side, well they're not going to see the same outcomes.