Why rectus abdominis is not proximal muscle?
It's not clear what "proximal" means in this context. It's not a standard use of that anatomical term in English. I'd also say that the figure on the left actually does show the pectoralis major.

The author of this figure might be trying to show the muscles that cross the proximal joints in the upper and lower limbs. For example:

Upper limb


Pectoralis major
Biceps brachii
Triceps brachii
Latissimus dorsi


Lower limb


Adductors (brevis, longus, magnus)
Rectus femoris
Semimembranosus, semitendinosus, biceps femoris (long head)
Gluteals (maximus, medius, minimus)


Muscles that do not cross the shoulder or hip are not included. This explains the lack of rectus abdominis or subclavius. Though it is not clear to me which the paired muscles in the posterior view are running craniocaudally from the thorax to the gluteal region.