system
Given the following post, respond as if you're commenting on Reddit:
human
[General]Why is it so rare for military sci-fi series to not depict promotions even after dozens of insane accomplishments?

For example, Mass Effect's Commander Shepard should have probably been skyrocketed to Flag Officer status after all he/she did in the first two games. Master Chief isn't even a Commissioned Officer I don't think when he really should be at least on the level of a senior ONI official. In Call of Duty, you're often saving the world and I don't recall you ever being more than a Sergeant or Lieutenant.  I know in Star Trek, Picard and Riker both rejected promotions which is fine but in most series the hero(oes) stay relatively low ranked in spite of being probably the most famous soldiers in their respective armies and navies. It's also a huge problem in anime where you have characters like Ichigo who never become a Captain and such like that.  It's weird and frustrating.

Edit: OK so thank you for the responses everyone. The consensus is that if the protagonist is promoted too greatly then they'll no longer be an interesting protagonist since they're mostly an admin and logistics person, and that great soldiers do not always make great leaders.
gpt
John-117 AKA Master Chief was promoted to Master Chief Petty Officer, the highest enlisted rank possible in the Navy, a few years into the war so that he could have some command over troops. The issue is that jumping from an enlisted rank to commissioned rank is incredibly rare to happen. His feats prior to Halo CE didn't warrant that promotion. 

Master Chief's widely known accomplishments (Halos 1-3) were in a relatively short amount of time.  These games happen over the course of 3-4 months, of which about 50% is just travelling through Slipspace. There really wasn't time to properly promote him during the games. 

After Halo 4, in the Halo comics series *Escalation*, Lord Hood even tells him that he could be made into an admiral, no questions asked, because of his accomplishments. Chief declines  saying " 'The Admiral' doesn't have quite the same ring to it." 

Post-war there was a change in the UNSC command structure, with the UNSC creating a new military branch called Spartan Operations. Spartans now have their only ranking system with each rank having a UNSC authority equivalent: Spartan-First Lieutenant, Fireteam Leader-Captain, Mission Handler-Major, Spartan Commander-Colonel, and Director of Spartan Operations/Commander-in-Chief of Spartans (CINCSPAR)-General.