Photos taken for black products always feel not black enough. What is the reason? Is the light or the camera not adjusted properly?

The camera measures black light, because the reflectivity of black light is low, the camera will misjudge it as underexposure, which will automatically increase the exposure and cause the black light to turn gray.

To reduce the exposure compensation (generally negative 1-2EV), a more accurate method is to calibrate photometry with a gray card in a photographic environment.