But I don't see the point in lowering the already poor brightness for regular Hell on Earth players. No one will put themselves in obviously losing conditions
Kind of yes, although for self handicapping reasons or when I'm recording in a way to show off the survival horror component of the game -- I do, it makes sense when everything is dark, as it's supposed to.
But given that there are so many ways to brighten the game up on a PC, if one wanted to, I don't see how would you force people to play in the dark environment, where the night vision goggles are useful. One can use built-in game controls, one can use ReShade, one can use gaming monitors that are capable to drastically improve brightness/contrast levels, one can edit the UE3 texture settings, etc. Without forcing the darkness on everyone you can't really make the night vision useful. Except on consoles -- there you can dictate how the game is played to a higher degree.
In the end one can kind of rework it so it provides some other utility on top of visibility (as visibility is solved through brightness/contrast by most players), but that would be sort of unrealistic. They wanted it to have advantages when used, but also drawbacks, just like in real world.