But most of those interactions were about Kes facilitating the development of other characters....they weren't really about her development....the doctor is a real boy....Janeway is mummy....Tuvok is a wise Vulcan...Tom is a bad boy who will clash with Neelix but then build a friendship with him etc etc
but who is Kes?....i don't really know....she's that nice girl who...erm....yeah...walks the corridors being nice & stuff
Bingo. Kes was largely a device in the service of the other main characters who implicitly mattered more. She was cursed with otherness and never fully integrated into the cast of characters. All along the elephant in the room was the hint that her involvement on the ship was going to be temporary. Same goes with Neelix, and, big surprise*, he never left the Delta Quadrant either.
* - sarcasm.