Due to people's training backgrounds and particular athletic goals, they might only need to improve range of motion in their upper body.  Many disciplines build flexible legs and hips, but don't invest the same time in mobilizing above the waist.
Focusing a program on just the upper body has also enabled us to make a deeper, more comprehensive program than other full-body mobility online programs.  That said, we do also have a Lower Body program that can be combined to address total body range of motion development.  If you're interested in training both, you can save over 20% through buying the Complete Flexibility Foundations Bundle.