What reason did Napolitano give?
I saw the exchange a couple of days ago, on some Fox program. Nappy was using the meaning of the word "qualified" in the sense of constitutional and regulatory requirements. He claimed that since Attorneys General and even interim Attorneys General, must be approved by the Senate, Whittaker came from a job that did not require Senate approval. He did quietly admit at the end of the segment, that Trump had some 'wiggle room' in that Whittaker was, indeed approved by the Senate for his previous job as Iowa Assistant Attorney Genera.
Since then, no one else has brought up the Senate approval issue, except for confirmed Never Trumpers. Nappy will need his nappies once Whittaker reigns in the out of control Mueller team.
“What reason did Napolitano give?”
Probably because he doesn’t regularly appear on a cable news show. Unfortunately Trump seems to be drawn to hiring celebrity commentators like Guiliani.