And whom, pray tell, holds that view?
A couple of trainers with whom I have worked - and I am quite persuaded in the right circumstances.
Not wishing to cast any aspersions toward hangar cleaners and other people who do jobs that are sometimes dismissed as unimportant, but at some levels in an organisation training about SMS processes may be of little value or interest (for a variety of reasons). An auditor who asks your hangar cleaner what they think of the SMS may get a blank look in return; but ask them what they have to do if they see something unsafe and there may be a comprehensive and effective response. Likewise, ask an accountant what they think of the SMS and there may be a different answer to questions like 'how can your job affect safety?' or 'what is your role in keeping the aeroplanes [or whatever] safe?'
One of the biggest problems in implementing an effective SMS is that many safety practitioners try to wrap safety up into big words and excessively complex processes that confuse or bore people doing the day job. It ain't rocket science and many aviation organisations have been doing good SMS since long before the term got bandied around by today's crop of Safety Managers!