There are probably a number of things. It's hard sometimes for people who are not right in the middle of it. They're not absorbing and receiving communications about the election all the time. For instance, for me anyway, when we're in Canada and we're in election time, there's coverage every day, and we're really focused on it. If you're living elsewhere, you won't get the same exposure to it, and you won't get the same reminders. You're certainly not going to get the same exposure to the candidates in your riding and the specific ways it's playing out in the riding where you'd vote, because you're not living in that community.
You can look at the writing on the wall and think that your vote is probably not going to make a difference in the riding. The same type of thing that could deter a Canadian living in Canada from voting could also apply in the international context in the sense that you might not feel that you're going to make a difference.