What reason does Odysseus give Calypso for wanting to return to Penelope?

Odysseus' reasons for wanting to leave Calypso to return
to his wife Penelope are only partially expressed by Odysseus' own
words. 

In Homer’s The Odyssey, the
story’s hero, Odysseus, struggles for 20 years to make it home to
Ithaca.

Late in his journey, after losing all of his men,
Odysseus finds himself stuck on the island of the immortal sea-nymph Calypso. Calypso
takes great interest in Odysseus and wants to keep him for
herself.

Meanwhile, back in Ithaca, Penelope’s suitors
continue to harass her and plot against Telemachus.

Against
this backdrop, Athena addresses Zeus at a gathering of the gods, pleading on behalf of
the stranded Odysseus. Zeus then orders Hermes, the messenger, to fly to Calypso and
instruct her to set Odysseus free.

As the above post noted,
Odysseus himself does not have a lot to say about it beyond confirming that he wishes to
return to Penelope even though she is mortal and less “comely” than
Calypso.

However, Odysseus' own words are not the only
evidence of his desire to return home. It is also worth noting how the poet describes
Odysseus’ behavior just prior to learning that Calypso will release
him:

Him she
found sitting on the shore, and his eyes were never dry of tears, and his sweet life was
ebbing away, as he longed mournfully for his return, for the nymph was no longer
pleasing in his
sight. 

Although these are
the poet’s words and not those of Odysseus, they still show how Odysseus is affected by
his absence from Ithaca and Penelope. Despite living with the love of a beautiful
immortal, he still wishes to return to his home and wife. Although he doesn't explicitly
say so to Calypso, he no longer finds her "pleasing in sight." Of course, this also
implies that Odysseus has the usual male weakness for beautiful women, because he did
find her pleasing earlier in the story.