Why? It is a feature of the engine and should be similarly complex to place this node or that node depending on the need. Made a workaround: created SoundPlayer2D nodes as children of a separate path beside a Viewport / Camera2D path and now i have spatial 2D sound i needed.
EDIT: tricky part was positioning. Root viewport doesn't move so have to place sound nodes relative to root viewport same as the owner objects are relative to camera. Tried making SoundPlayer2D nodes children of Node2D and positioning just one node but no effect. So had to position every SoundPlayer2D via script.
EDIT2: tutorials on using 2D sound properly are non-existent. Had to guess and hit what i assume was a bug.