Whatever it is - you seem not to be comparing apples to apples.
One way to form a misunderstanding is to to learn only parts of how each system works and to overlook some important detail.
With both systems with the same aperture lens, both lenses wide open I and others have been unable to detect a screen difference in low light.
Nikon has the advantage or disadvantage of showing stopped down depth of field using apertures wider than wide open with lenses faster than f5.6.
If you put an f1.8 lens wide open on each system are you SURE you can see the difference you refer to. I cannot.
If you use the Nikon at f5.6 it shows f 5.6 depth of field and just over 3 stops less light transmission.
If you use the Canon at f5.6 you cannot normally see f5.6 depth of field.
Nikon gives you the choice as you can always view wide open.