The real question is: Why is an American diplomat criticizing a foreign ambassador for his choice of speaking engagements in America?

Because she is allowed to answer questions in a press interview and because the ambassador should stay out of domestic American politics and not join in a campaign to torpedo a rival to AIPAC. The way in which Oren acted as a faction leader in American Jewish politics, rather than as a neutral representative of his country, open to all people of good will toward Israel, was obnoxious and undiplomatic. And his position is of far more importance than Rosenthal's.