Well here is the thing, the Gamer Ability doesn't really awaken in them. Its just you are all going about your lives when you wake up one day and BOOM.

You all have it. You may have had it for a day or two, but it will just have happened without even realizing it. Like maybe you wake up and you hear your boss calling you to go do something after you wake up and a Quest Alert appears or you go outside and see people's names and levels floating over their head like in MMOs. 

I think its more interesting and not cliche "oh we all suddenly met this dude or did this thing and now we all have this power) if you all just sort of have it (like how it is in the Manwha). 

It also adds more mystery if you don't know HOW it happened.