I'm just a poli-sci guy from Saskatchewan, but maybe I can provide a bit of insight on this one...hopefully this is in-depth enough, and not too blathering. I'll do my best to answer any follow-ups as I can as well.

I'll focus mostly on Saskatchewan, since that tends to be my more informed area..If anyone wants to cover Alberta, then please fill in by all means. I can't really speak to other countries either.

The short answer is a combination of Western Populism and Right-Wing Vote splitting. While Saskatchewan was flirting with populism on the left, under the CCF, Alberta was doing the same with the right under the Social Credit party. What both of these organizations had in common was that they spoke to generalized concerns and proposed solutions that the 'common man' saw as a good answer. In Saskatchewan, the CCF (forerunner to the NDP) under Douglas was bolstered by the fact that it was a collective of labour-farmers, which in an agrarian province like Saskatchewan, provided a pretty solid base.

Up until Douglas' election, I think it's important to keep some facts about the rural parts of the province in mind. When Douglas came to power in 1944, Saskatchewan was a very different place. The entire province had only 222km of surfaced roads; by contrast, Saskatchewan in 2003 had 29,000km of paved road and 228,000km road paved/unpaved more than any other province in Canada. Douglas undertook expansion of surfaced/paved roads, including the completion of the Saskatchewan portion of the Trans-Canada Highway; of which, Saskatchewan was the first province to complete their portion of the nation spanning road.

Prior to 1949, only about 1% of rural Saskatchewan farms were powered by electricity. By the end of 1956, Douglas' government had connected about 47% of Saskatchewan's rural farms to electricity, along with other rural communities outside of farms.

The reason to keep things like this in mind is to highlight what a different place the province was when Douglas came to power, and what a different place it was by the time Woodrow Lloyd lost to Ross Thatcher. Thatcher is one of those figures I like to call attention to, as if history tends to repeat itself, he is a perfect parallel for Brad Wall in the future. (But that's another subject.)

Under Douglas, Saskatchewan changed as listed above, but also this meant that taxes were high to compensate for social spending. And while the Social Credit Party in Alberta experienced electoral success, it never formed government in Saskatchewan...BUT it did enjoy a good degree of support within the province. At least, until the 1964 provincial election; wherein the party imploded and only managed to run 2 candidates in the entire province. Thatcher's Liberals were the beneficiary of Social Credit's collapse as they became the 'go-to' anti-Socialist vote in the province. If you didn't support the CCF, then you were likely voting Liberal.

Thatcher campaigned on the EXACTLY the same kind of rhetoric you see today: The 'socialists' have taxes too high, they scare aware 'private business and investment', and they make cost of living too expense for the everyday person. Add to this some fallout from the Doctor's Strike in establishing medicare, and Lloyd not quite having Douglas' personal popularity, and the CCF narrowly lost the 1964 election.

In what has become a 'trademark' line for pretty much all centre-right and right politicians upon being elected, Thatcher declared that Saskatchewan 'was open for business' once again. (Grant Devine, Brad Wall, Doug Ford, and other centre-right Premiers across Canada have made such declarations upon electoral success since.)

With this history in mind, I'll shift now to the federal sphere of things. In 1957, the CCF dominated Saskatchewan's federal seats holding 10 of the 17 seats the province had. Just a year later, in 1958, the CCF lost all but 1 seat as Diefenbaker's Progressive Conservatives swept the other 16. Part of this, much like the provincial counterpart would follow in 1964, was the collapse of the federal Social Credit Party. Diefenbaker's popularity, and status as a Saskatchewan 'native son', compounded the issue and definitely helped provide a boost for the PCs in the province. And with the collapse of Social Credit, vote splitting that had previously helped the CCF/NDP in the province disappeared and allowed for the PCs to end up with the largest majority in Canadian history (up until Brian Mulroney.)

1962 wasn't much better as the CCF was shut out completely in Saskatchewan; partially due to the provincial strife over the Doctor's Strike and the rocky start of medicare within the province. Douglas himself lost his election in Regina, and went out to BC to gain a seat federally. Diefenbaker's Tories would continue to hold the province's seats in almost complete uniformity until 1968. But even after Diefenbaker left office, the Tories would usually have the majority result in the province, though not completely control every last seat.

It wouldn't be until 1988 that the NDP would carry the majority of Saskatchewan's seats federally under Ed Broadbent, when the party captured 10 of the province's 14 seats.

By 1993, the federal split would see the NDP dropped to 5 of the 14 seats, with Liberals and the burgeoning Reform Party capturing the others. By 1997, the Reform Party would hold the majority of seats with 8, and then would progressive grow that majority up until today, and under their rebranding as the Conservative Party.

The common wisdom is that the growth of the Reform Party, an expansion on that theme of western populism, was what put the nail in the coffin of the left-leaning federal NDP in Saskatchewan. And that is partially true; the NDP suffered federal in the province due to their support of the Charlottetown Accord as the Reform Party became the voice of anti-Charlottetown rhetoric in the west. The party, along with other commentators, began to make the still used argument that Charlottetown would 'cement Canadian power in Ontario-Quebec' and 'leave the West out'. (Further used when Reform would campaign under the slogan of 'The West Wants In').

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Wow, I feel like I owe you a semester's worth of tuition for that answer! Thanks so much for the deep dive.