I dispute your "much of Ontario"—Northern Ontario is larger, areawise, than Southern Ontario, and everything north of and including Parry Sound has a subzero average December temperature. Lakes do freeze over in December up here—maybe not enough that it's safe to walk out to the center of the larger ones, but in a normal year the ice would be solid enough by now that you could walk or take a skidoo some distance from shore.

The real issue, though, is people doing "what they've always done" at this time of year and paying more attention to the calendar dates than the exceptionally high temperatures we've been having.

(An entire family went through the ice on an ATV recently and may be among the deaths counted in the article—I think it was over near the Sault. Normally the ice would have been able to support them. This year it didn't.)