Why isn't lipo 360° for arms common?

Although liposuction may seen "easy" to those who have minimal training in more advanced surgical techniques (such as physicians who are not trained in plastic surgery), there are a lot of patients who are interested in liposuction who are not good candidates for it. Liposuction removes fat from under the skin but after the fat is removed the skin needs to be able to contract, if the skin is loose prior to liposuction it will be even more loose and have more wrinkles after.
In my experience, the majority of people who have concerns about their arms and are seeking a procedure to improve the appearance would benefit from a brachioplasty, and liposuction only would make the arms look worse. There are definitely a lot of people who would be good candidates for arm liposuction, but they also would likely gain similar results from weight loss. This could be achieved with medications such as ozempic or mounjaro. All these factors are likely why you don't see many advertisements or prices on arm liposuction.
Hope this helps!