Why is the mobile phone video particularly dark at night?

Photography mode is related to aperture and exposure time. Even if the light is dim, the program can achieve full exposure by increasing the aperture or extending the exposure time (mobile phones usually do this by extending the exposure time, but in this case it is easy to blur the photos).

Video is real-time lighting, so there is no time to accumulate enough exposure, so it will be very dark. The camera must fill the light!

Don't make an analogy, the lighting principle of photography and video recording is very different.