most arterial road lanes in Toronto have already been narrowed. There aren't a whole lot of streets left with excessive road lanes, and in most cases the space savings are not enough for cycle lanes as it results in only a few centimetres saved!
Excessive lane widths is more of a problem in the 905, which generally has a long way to go on that front.
I agree that it should generally be done on the few arterials that haven't yet had their lanes narrowed, though. A quick look at Ellesmere Road through it's 6-lane section shows it could potentially be modified to 3.2m lanes and have enough space left over for protected bike lanes on both sides, for example.