Plastic's expensive for small runs- the injection mould process is very setup intensive. That's why most aftermarket parts are fibreglass.
David makes a good point about legality, but then his legal indicators seem to be peeking round the side of an illegal number plate
He's absolutely right of course, but I can't remember ever hearing of anyone being stopped for having their indicators too close together. Though combining close together indicators with rubbish visibility is asking for trouble I'm sure, that's why I dislike the Ermax on.