This lovely sign is clearly intended to do more than express a truism. Of course it’s true that you, dear boater, are responsible for physically causing the wake your boat leaves. After all, who else could be?
The emphasis, it seems to me, is on the notion of personal moral responsibility. It’s a reminder with the tone of advice from a kindly uncle. “Look, kid. Take it from me. There’s no getting around it. YOU are responsible for what you do. No one else can be!” (It also reminds me of the old Smokey The Bear line: “Only YOU can stop forest fires.”