"...an event because they have judged the other members would appreciate the knowledge... "
If we're talking most of the other members, or a sizeable proportion of the other members, then that pretty much restricts it to audaxes only.
But I think sportive promoters feel it ok to advertise here simply because they believe that there will be some people, however much a minority they are, that would appreciate the knowledge. As far as they're concerned, if their post draws in just one person to ride their event, then since pixels don't cost, and anyone not interested can simply not read it, then it's been worth it. So given that, and because there isn't (currently) a rule saying they shouldn't, we can't really blame them for doing so.