The Tories implemented massive subsidies of the oil industry which resulted in huge overbuilding, turning Canada into a one trick pony.
Everyone spoke about the dangers at the time, a volatile currency is destructive to manufacturing and results in an economy that is entirely dependent on oil.
People think the low dollar now will benefit manufacturing, but it won't. Manufacturing is capital intensive, you have to invest millions in machinery that then takes years to pay off and become profitable.
In that context investors take a long term view, and with a highly volatile currency it is too risky. While existing facilities benefit from the low dollar no one will build new manufacturing capabilities in an economy where the petro dollar makes it impossible to predict future profitability.