He didn't realise that he could just ask. And being a good boy he didn't want to appear pushy.

Quark went ahead and filed that complaint about his anti-Ferengi remarks just before Voyager went MIA. Janeway takes bigotry very seriously.

He didn't commit enough war crimes (lacks leadership mindset)

Simply not enough pips on board the ship.

Sometimes you have an employee that is so good at their job you never want to replace them

Garrett Wang repeatedly turned down Rick Berman's sexual advances

No one under him is qualified for bridge crew. Every single person not named in the credits on Voyager is completely incompetent. Promote Kim and you have to promote crewman Bushnell who thinks Warp drive opens a portal to hell everytime, smells awful and calls all women "females".

If you promote him then he’s just going to take the title and leave for more money.

DEI was banned so only white dudes, and people who banged the captain, got promoted.

He had more romantic chemistry with Seven than Janeway was willing to tolerate.

They needed to keep at least ONE ensign around, and all the others got promoted or died.

Tom told Janeway it'd be funny if the EMH out ranked him while giving her a fresh pot of coffee.

He secretly works for Starfleet's Internal Affairs and uses his position to spy on Janeway et al.

Janeway actually did try to promote him, but he overslept and missed the promotion ceremony.

No virgin lieutenants allowed in Starfleet

Pips can't be replicated and Voyager only had a limited supply of spares. Janeway set aside the only spare pip for the bridge crew for Tuvok's eventual promotion.

There was one time before they even got into the Delta quadrant that Kim took the last pot of coffee and didn't make more.

Ships need ensigns to run, at least one. He was the One.

The unions in Star Fleet are actually controlled by the Dominion, and as such they are ineffectual by design. Harry doesn’t know this, of course

Because he was an experimental ensign.

Starfleet had deliberately trained him wrong, as a joke.

Janeway simply forgot to.

Oh wait, you said wrong answers…

He was bad at his job and did nothing to deserve an extra pip.

/s because my conscious can’t handle stating this otherwise.

The promotion pip was continuously traded for coffee rations

His first name isn't really Harry, it's Hitler. Once Starfleet learned the truth, it realized it could never promote him for fear the secret would come out.

Because he didn't go Transwarp, turn into a space salamander and have squigglings with the Captain?

At the bar celebrating his new commission aboard Voyager he met an ensign named Mariner.

Shortly after he was hired , he said he had always looked up to Captain Picard. That never sat right with her.

He put cream into the Captain's coffee once and she never forgave him.

Because of legal complications of being from a duplicate voyager post "Deadlock" he couldn't be promoted further than ensign.

Every time you die, or are replaced by something like an alternate universe duplicate, your seniority resets