Thanks for the explanation and further background! I appreciate it. I'm still a little confused why custom OS is needed for a headset. I would have guessed you'd just need another...I forget the term for it, but on Linux you have like XFCE, Cinnamon, and KDE like GUI skins on top of the core functionality.
Reading between the lines, it sounds like they can get better performance on the target hardware with a purpose-built design. It is about more than the GUI.