Well, it kind of was Tory for a small while in the post-war period.
You will get mountains of people in this thread saying "Abort teh SNP yeah fer sure", and tons of other people saying "Abort teh Thatcher yeah fer sure", but Scotland has never been good ground for the Tories, ever. This goes back hundreds of years, way back into the 19th century, when they were regularly outfought by the Liberals.
When you look at things in the round, you realise the post-war '55 spike was a blip; they managed that by the collapse of the Liberals and their annexation of the National Liberal vote in Scotland. Probably the last gasp of the Orange vote also helped. Their early post-war strength was therefore deeply artificial, there was no real long-term structural underpinning to it. The decline of the Tory vote in Scotland pre-dates both the big Nationalist bang of the seventies and Thatcher.
I think there are things you can do to arrest the decline, and probably avoid the extinction of Toryism in Scotland, (Kill off the Liberals in the fifties, keep the Tories One Nation and devolutionist, etc) but I don't believe for a moment that you can make them permanently dominant in Scotland.