Why most of the microphones are placed on the left of headsets / headphones?

I've noticed that the mayority of the well-known brands (Sennheiser, Logitech, Plantronics, Razer, SteelSeries, Audio-Technica, Phillips, etc) tend to make headsets with the microphone on the left, is there any UX related reason for that tendency? If not, what's the reason of that choice?

The position of the mic would be equidistant to the the mouth when placed on the right side, so there's no difference when recording.

My improbable theories:

1) Maybe it could be useful for people who eat (or make something using with their right hand and mouth, like smoking) while wearing their headphones, supposing that the person is right-handed(what it's true in most cases) and the mic is neither in front nor too close to their mouth.

2) I think we usually align our body more to the left side of the keyboard (centered between 'g' and 'h' keys or so, and probably to center of monitor too, to avoid neck tension) for writing comfortably, and right-handed ones place the mouse on the right, so the mic on the left could go along with the "left side weight" and avoiding the possible sensation of the microphone "being in the middle". This theory is enhanced in the case that the cable is not divided in two to reach each side and just reach the side where the microphone is placed, so the cord will hang closer to that side and not centered to your body.