That made sense when commodity prices were high and there was an oil boom in Alberta sucking away construction workers. I would think prices would be lower now..
Very true, but cost escalation is a pretty complicated thing. Falling commodities prices help, and while the raw material costs of glass and aluminium and steel might be lower, the prices to manipulate those raw materials into useful things are still increasing. Labour, transportation, and energy prices play a big role here.
And while it is true that the oil boom certainly play a part in draining workers across Canada, that has been less of an issue in Ontario than in other provinces because of the pronounced building boom in the GTA. There is still a lot of demand for technologists, engineers, project managers, trade workers, etc, and a big shortage in the talent pool. The US market is also quite busy right now, and especially with the falling Loonie, this is sucking away the time and talent of many professional firms who are landing contracts down south.
Another thing to not forget is that a high-demand market creates supply-chain bottlenecks, meaning delayed production slots and higher prices commanded by the suppliers. Never forget that every construction trade that you see on-site is supplied by a network of dozens, if not hundreds of smaller suppliers.
There are also less obvious issues, such as clients requiring extended warranties much more often than in the past, where standard warranty periods were okay. Or the rising cost of liability insurance.