Poor Harry. All the responsibility and none of the rank.
They would have promoted him except he was always late for his pip ceremony due to oversleeping.
Janeway: "Congratulations, Lieutenant."
Kim: (rolls over) "Five more minutes..."
Janeway: *pip yoink* "Did I say lieutenant? I meant ensign...that's for being tardy."
Besides, it's a slippery slope to Admiral, where nobody lets you have fun anymore.