Probably being discontinued because they are not resistor spark plugs, even on our motorised bikes I have been recommending the NGK-BR6HS, (which is the replacement for the non-resistor plugs), for some years now because the speedometers are mostly wireless bike computers right now and the non-resistor plugs with RF interference gives false readings...Before I changed to the resistor plugs, my bike computer was telling me I was doing 99 MPH whilst stopped at a stop sign...lol...lol.