They could advertise a game for lots of reasons. Could be Nintendo offered matching advertising dollars. I seem a lot of wii games advertised lately, not just COD WAW.
I doubt that it was because it started selling more. It basic economics that you advertise to increase selling, not because it is already selling. If something doesn't sell on it's own you advertise, if that doesn't work you lower prices.
It takes time for marketing campaigns. Maybe they decided to advertise because the reviews came in decent (in the 80s), and figured advertising would be more effective.








