As detailed in the video above (See from 02:50), if the deep core/abdominal pressure is weak, the rib cage goes down and this naturally brings the neck and shoulders down and forward.

As shoulders roll in with elbows bent, the triceps muscles naturally sit in a lengthened position. Then, it is easy to get weak and weak muscles tend to get overloaded and tight (Yellow arrows). Tight muscles pull its tendon away from the bone (Purple arrow), which increases tension. This increased tension can cause friction between the tendon and bone, resulting in tendon problems.

Moreover, the triceps muscle is connected to the infraspinatus muscle (See 1st image below) on the back of shoulder that also gets weak when the shoulder is rolled in. Then, the triceps have to work harder to compensate as they work together through the deep back arm line (2nd image). Therefore, this program not only focuses on restoring the function of these muscles but also correcting any postural imbalance like rounded shoulders.