Why are they called "old kamma"?

The sutta below states that eyes, ears, nose, tongue, body and mind are old kamma. Why are these called old kamma (*purāṇakammā*)? Is it because of rebirth? Or could there be other reasons? If rebirth is the only reason, then I feel that this explanation seems too simple. From SN 35.146 : > And what is old kamma? > > The eye is old kamma. It should be seen as produced by choices and > intentions, as something to be felt. > > The ear … nose … tongue … body … mind is old kamma. It should be seen > as produced by choices and intentions, as something to be felt. > > This is called old kamma. > > And what is new kamma? > > The deeds you currently perform by way of body, speech, and mind. > > This is called new kamma. (I replaced "action" with "kamma")