In Germany there is a legal reqirement that all new bikes have to be sold fitted with a dynamo and lights, with the exception of bikes under a certain weight limit (around 11kg?) which are classed as racing bikes (so basically road bikes and some MTBs), and which are permitted to use battery lights.Why don't they just fit all bikes with lights as standard? Same with cars, it's a legal requirement to have them and if you want to change them later to something different or better then you can.
I'm not convinced of the merits of this law, yes, it does mean that most bikes have lights fitted, but on the other hand you still get to hear the usual moaning about all those bloody invisible unlit cyclists, pay no road tax, should be licensed bla bla bla