Easy. the price volatility is a red herring. The real curse is that the UK already rode the peak of production, but the average of all North Sea fields is now in terminal decline.
In particular, you will spend more and more money (currently about 8bn OPEX/yr and growing [0]) but only get a declining production: lately about -5% less oil/yr [1]). There are still many billions to be made, but it won't fuel _growth_ in Scotland. (the link you provided explains how the UK already took that opportunity)
[0] http://euanmearns.com/uk-north-sea-oil-production-decline/
[1] http://cdn.static-economist.com/sites/default/files/imagecac...