system
Given the following post, respond as if you're commenting on Reddit:
human
[Star Trek Voyager] Why is Harry Kim an ensign for so long?

Ensign Kim is considered a senior officer for meetings, he's bridge staff, and he eventually commands the night watch. So why isn't he promoted? 

One reason I thought of is that they have to maintain a balance of ranks, but there were other promotions (like Tuvok) and a demotion *to* ensign (Tom Paris), which would seem to open up a lieutenant position on the bridge.
gpt
*Voyager*, though taking casualties on its journey, presumably did not lose enough crew to warrant promoting people outside their positions. With nobody to replace them from their lower ranks, Janeway would be faced with twelve Lieutenant Commanders and not enough Ensigns beneath them- let alone non-commissioned crew. 

Harry did have senior ranking and was given the proper respect due to his experience, but could not be moved out of his position- the crew was already made up and sorted. Perhaps things could change as crew members were lost, but the bridge crew was mostly safe through the journey and thus did not allow for promotions very often. However, given his specific branch, it's likely that Ops simply did not have many openings and was a stagnant line.