Question

why do you think that pinna is immovable in human being unlike in most other mammals

Answer 1

because its stiff in us as compared to other mammals so it is immovable

Answer 2

Ear movement is common in many mammals, including cats, dogs and horses, and usually serves to swivel the ear towards the direction of a sound. A group of muscles called the auriculares are responsible for this movement. This group includes: the auricularis anterior, which draws the ear up and forward; the auricularis superior, which raises it; and the auricularis posterior, which pulls it backwards. In humans, ear wiggling is a vestigial feature, which means it is a trait that was useful in ancestral creatures but that eventually became functionless