Skullwaker on 06 July 2015
Some games just have more dedicated fanbases. For example, JRPGs like Final Fantasy or Xenoblade will have most of their sales in the first month or so, and that's because most people that want the game will get it right then and there.
On the other hand, there are certain games like Mario Kart or Minecraft that are more likely to be picked up at any given time due to their accessibility and longevity (Mario Kart is once per console gen, there is only one Minecraft).
Basically, target audience, genre and competition are major factors in the legs of a game.
