Why it is Respawn refuses to address the actual cause of third partying?

This is actually incorrect I think the release of KC season 1 proves this more than words could.
Look how much people fight and long distance sound isnt required.

The core issue is not just sound travel distance. It is also the fact that respawn have continually made maps require less skill to play and to make third partying easier.
Its that age old thing of you goto make it so even the worse players in your game can win and sadly third partying is a heavy result of this. Why ingage a 3v3 when you can just sit back with a charge rifle , 301, or G7 and just get easy free kills.

Look at season 1,
Any one who played when this game first came out understood snipers were strong but you never used them just to third party. They were a viable weapon that allowed you get the early damage then push. Respawn then started making the maps more open and with less cover so now all that happens is people wont push they wont fight because instead of having 20 places of cover in a 200m radius you now have a single building and a tree. Its half the reason Rev/Oct has become such an issue also. 

Honestly I think KC Skulltown shows what a great area is. Its built up there is loads of places to fight, different levels, multiple ways to attack or hold. Now look at KC now its an open mess where all you do is wait for an oct/rev squad to jump from halfway across the map