"Full time" is a bit of catch-all, though.

Rather like Frequent Miler, I don't have another job at the moment but I certainly don't consider Head for Points anything like a full-time occupation!

I would guess that Ben, having just graduated, realised the money was more than he would get from a real job and so didn't see the need. Gary, on the other hand (and this is continued guessing) already has a good job he likes and sticks with it, even if he doesn't need to (he is also older and probably has a better grasp of how easily the card bonuses etc could disappear).