Why do some surgeons prefer not to place an arm lift scar along the tricep/bicep line?

Typically the incision for the arm lift is along the inner arm. This is to best disguise the scar as it will be hidden when the patient has their arms at the side. I've included a video that I hope you find helpful about this procedure as well as the scars that are associated with it.

The position of the incision is chosen to make the resulting scar as inconspicuous as possible. The 2 most common locations are down the back of the arm or on the inside of the arm. Surgeons and patients choose the location they think will be hidden the best.
1. Back of the arm When an incision is down the back of the arm the scar tends to be more visible from the back when your arm is resting at your side. These scars tend to be less noticeable when your arm is out to the side, as if you are waving. In this position the patient rarely sees the scar but someone standing behind you would notice it.
2. Inside the arm When an incision is on the inside of the arm the resulting scar tends to be less visible when your arm is resting at your side and more visible when you are waving.
There is also the possibility of placing an incision somewhere between the two locations described. This is still considered to be on the inside of the arm and has some of the benefits and down sides to each of the places described above
In the end there is no "best" location. I prefer inactions on the inside of the arms but it is really a matter of the preference for the patient. When you have a consult with your plastic surgeon