George Takei pushed for his character to get a promotion. By doing so, he also basically ensured that he would not be part of the main action of the film and cut his screen time. Not the best move.
Uhura was criminally underused throughout the films in general, but the same was true in the series.
Chekov fared a little better at least. We saw less stagnation from him than we did from the other characters. He was chief of security in TMP, then he was first officer of the Reliant in TWOK, then he took on both communications and science officer roles to help his friends in TSFS, and then he got some really good scenes in TVH. Unfortunately, he was back at his navigator station in TFF and TUC, which made absolutely no sense.