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 &quot;action&quot; with &quot;kamma&quot;)
Piya Tan says, though I'm not sure this is clear,

“Old karma”
here refers to the six senses. The theme of “old karma” (purana,kamma) is applied to the body (synonymous with the six senses) in the (Kaya) Na Tumha Sutta (S 12.37/2:64 f), where the Anguttara Commentary explains that the body is not “old karma” but because it arises from old karma, it is referred to in
terms of its conditions. It is seen as “put together” (abhisankhata) since it is created by conditions. It is
“thought out” (abhisañcetayita) because it is based on volition (the will), rooted in volition. It is “to be
felt” (vedaniya) because it is basis for what is to be felt [ie the basis and object for feeling] (SA 2:70,
402).

Perhaps the idea is that people are born of (heir to) their kamma.
The summary on this page (I'm not sure who's the author, perhaps Ven Sujato) summarises this sutta as,

The six interior sense fields are not yours, but are old kamma, generated by choices in past lives. This is explained in terms of the four noble truths.