Ah, yes, Apathy...
... Our countries leading cause of, whatever…
and I don't think you will find it's just woodturning clubs. Member participation is a difficult thing to get. In assisting at Shows, doing demonstrations, Hands On stands, you name it, you can probably already name the few that will volunteer to do or assist.
Some people don't think they are good enough, some are too embarrassed, some think they have nothing to show or say, some just won't.
I have no more answer than anyone else, but I have found that gentle cajoling when someone has something to offer, a skill, understanding or particular ability, that could be shared, helps.
I've also tutored people who might to give them the confidence to do a small demo, and once they get a taste for it, they often have a second go.