Why? Why not when we have other abilities that stun enemies, and even open them up to finishers. Take Inaros 1st abilithy for example. Good range, OK duration, very good stun and opens up enemies to finishers. Oh, and it's dirt cheap to cast. Then we have Ember's Accelerant, which is also recastable and can be used to permastun enemies if need be. Need I go on?
Edit: Banshee will recieve a new passive soon.
"All weapons will be silent".
This literally makes Silence a 75