There are a of reasons why this happens. Film cannot correct for green fluorescent lights, yellow tungsten bulbs, dark shadows, high low contrast, etc., and is entirely dependent on the photographer to make the corrections that our brains and eyes make for us automatically. The whole goal of photography is to be able to record on film what you are seeing in your mind. There are plenty of tools to help photographers do just that. If I have left out your favorite misconception, or if I have made you more confused, please let me know.
Life is too short to spend wondering why they sell lights for darkrooms.