It is larger than all of the other items.
Its color contrasts with the other colors in the picture, making it standout.
The advertiser uses hierarchy in his design.
If you want something to stand out, making it bigger is the simplest answer possible.
By adding contrast, you create a sense of separation between what you want to expose and the rest. Being the rest, in this case, the most dominant aspect (as in, a black screen and a white ball in the middle of it, the white ball will get more attention).
Hierarchy in Design is a way of combining elements of visual design to guide the eyes of who is looking at the ad, commercial or whatever the piece is. By making things diminish size or change colors in an specific order, you can ensure that the target will look at where you want him or she to look at.