Unless I'm missing something you'd have thought they would allow for more options.
They're happy for us to stick all sorts of reflectors on helmets, jackets, pants, rear/front of the bike, etc etc.. so as to increase our chances to be seen by other drivers, but the regulation seems to be very restrictive as to what lights you can use; lights that would surely be more effective as they are not dependent on other light sources.
There are obviously colours you need to stick to and you shouldn't use anything that could endanger/blind other road users, but still.
The following is an over-the-top/extreme example but it would surely make a bike more visible.