Why not recording full hd video at wide and zooming in (like the camera does) when ever you want ... maybe because this means that the phone has to capture video at 8 megapixel and then downgrade it at Full HD. So this must be more CPU demanding.
Probably the phone records video at 1920x1080 using the center of the sensor. Capturing only the center of the sensor does the zoom effect. I cant think another reason why loosing the wide angle.
The narrow field of view is useful in some cases (maybe outside) but recording inside rooms everything is very close...