Your lights are broken?

This may be a daft question, but… Why do manufacturers insist on only illuminating one side of a bikes lights?

My last bike was a Kawasaki 2007 Z750 and I would be a rich man today if I had a penny for every time someone said to me ‘your lights are broken’.

Last month I was lucky enough to trade up to a new ZX10R. Again last night the first person has started the ball rolling and said ‘one of you lights is broken’.

It’s so annoying that I’m going to look into having both sides on low beam.

Is this a fashion statement or is it because the battery would not be powerful enough to sustain prolonged use of two bulbs?