They insist on having completely different laws for every little thing. From a companies POV, its probably as legally onerous as operating in a different country altogether - not worth it.
It's much worse than that. Google didn't research the sweepstakes laws in, say, Paraguay or the Gambia before making this announcement. They figure that, in the worst case, their legal department will tell them not to award the prize if the winner comes from a country where they can't legally award it, and they'll scramble the necessary PR people if that comes to pass.
For Quebec, on the other hand, they'll be forbidden from carrying on business in all of Canada if they advertise this competition as one that can be won in Quebec. A terrible chilling effect - and I say this as someone who universally favours the freedom and self-determination of small nations such as Quebec.
For an American firm especially, it's just a odd little place with everything in a different language, it's just not worth the hassle for lawyers and risk, so they just skip it.