The reason being that when units are thrown into the air (likely to become increasingly common with lighter infantry units such as in SWTA, and the new mass tags), they look quite silly. This could be very easily remedied through the use of the walking animation (perhaps played at double speed), which would make the units flail while in the air.
Its a minor alteration, and I think it would add quite a lot of character, as well as customizeability.
In order to reinforce my point, I present to you, exhibit A:

(Image by SecurE)
As you can see, our stormtrooper appears to be attempting to pull a complex olympic diving move by remaining absolutely rigid as he is flung into the air.