I have half-an-idea why this might be the case.
My theory runs that there is potential for confusion over the role, caused by the fact that the lighting designer in amateur theatre is often the amateur lighting designer/rigger/cabler/focuser/programmer/pluggerinner/operator – or in other words the boy or girl in black who knows how it all works; the lampie geek that can make it all sing to his or her tune. In some cases I dare say that is the major motivation for the person in that role too – they get their kicks by plugging maximum stuff up, powering up, pointing it in the right direction, triumphing over the desk and seeing how many cues they can fit into the show for a given (always tight) timeframe. I cannot deny the fascination in that.
But equally I’m sure there are plenty of examples where the amateur lighting designer is interested in painting pictures, in creating moods and in ensuring that the drama, excitement and presence on stage transmits with maximum effect betwixt cast and audience. That’s me too. I always want to be an intrinsic part of the production team, engaged in the earliest possible stages of a show to understand what is being created and to provide guidance where required as well as sweating out its always frantic final run ins.
Is the role any more important than the director, producer, MD, designer, choreographer, stage manager or costumier? No of course not. But just as a production would look a bit sick without direction, the cast a bit boring without costumes and a musical completely pointless without music, I’d argue it would all look pretty awful too in most cases without being creatively (and often simply) lit.