Why, on foxeye designs - only one of two headlights on, on dipped beam?

[SteveMc278]

Foxeye FZS600 Mk2 has both headlights on, on dipped beam,...so does FZS1000 Gen1,...so does Suz SV650S,...and possibly there are other bikes that have both (foxeye) headlights on, on dipped beam.
Stacked headlights are a logical design in which it makes sense if manufacturers don't want to utilise both headlight housings for dipped beam whereas foxeye designs with only one light on just look wrong,..as if one light is faulty.....and loads of bikes are designed like this  ..............Why?