It's not running, it's strategic withdrawal. Al-Shabab are clearly versed in their Sun Tzu, facing an army who is superior numerically and has more advanced weaponry is suicidal, naturally, the rational thing to do is leave the proximity of the Woyane and attempt to draw them into Shabab territory with terrain that will aid them in guerrilla warfare. Why would they stray from a tried and tested tactic which has already earned them one victory against the Agame government?
Thank Allah a genius like our Amir in Tora Bora is controlling the Mujahid and not your ilk
You must realize the Ethiopian forces are in disarray and have been for centuries, due to their population they have large numbers but that's worthless if they're poorly trained. An excellent example is Eritrea's military victory led by the Lion of Nakfa.