Why do I have to dust so often?

As soon as I dust, I turn around and there’s a layer of dust on the piano again. If I kept my house looking newly dusted, I’d have to do it every single day. Could there be one place it’s coming from that I’m not aware of?

My husband regularly changes the air filter. I also vacuum regularly; about three times a week. Is this normal? We have one cat and a toddler (those filthy beasts!).