Excuse Me and God Bless You

How come when someone sneezes, 5 people instantly yell “God bless you,” but if they burp or fart, if anyone says anything, it’s “Excuse yourself.” Those all seem about the same to me. And how come coughing gets left out? That doesn’t seem fair. Maybe I can start a trend where, whenever someone coughs, we’ll all agree to say, “Robitussin!”