Simple question really. Why do these cameras use micro four thirds?
About Four Thirds system:
Before wide screen (16:9) monitors and televisions were popular, 4:3 monitors/televisions as the norm; so I guess it seems normal to have sensors which are compatible.
The Micro Four Thirds system has a shorter registration distance (a/k/a flange focal distance), to reduce the weight (and price) for cameras, but uses the same sensor size and 4:3 aspect ratio.