If society preys on philosopher poets, we don't get philosophy or poetry, our ethics never develops, and the fundamental principles of society don't improve, limiting how much technological progress can raise the standard of living. I personally call that a bad outcome.
Social philosophy influences societal change, by providing ideas. Without philosophers, activists have to be more visionary than they already are, making them rarer.
(Moral philosophy, not really, I'll agree with you.)
Why do you say understanding isn't a driver of change? It seems to be pretty important to me.
You kind of put your foot in it with this comment. Societal change, for the most part, directly follows questioning and understanding.