The problem with night mode is that it compresses the dynamic range of the audio which undermines one of the main benefits of having a home theater system. It's a poor compromise for bad audio mixing.
Manually turning the volume up and down is literally compressing the dynamic range; that's the goal here.
Most home theater systems are in a home where the noise floor is significantly higher than a theater, which the audio mix was targeting. Dynamic range compression is often appropriate and when applied correctly improves the experience in homes.