Audio-only calls have a better host experience than guest experience.
The host only has the session bar, and that session bar will sit on top of all other windows (making it easier to toggle camera/mute &c.)
By contrast, the guest sees the session bar within a large useless empty window. Aside from obscuring the view of their other apps, the guest
also
has their session bar constrained to this window, meaning that they can't follow the pattern of opening the session bar with a keyboard shortcut and then clicking the microphone toggle -- first they have to focus the window.
It would be great for audio-only calls to remove the window for guests and have their experience mirror the host experience.