Movies have dark scenes nowadays mainly because it is a trend. On top of that dark scenes can have practical advantages (set building, VFX, lighting, etc. can be reduced or become much simpler to do which directly translates into money saved during shooting).
If I had to guess, the trend of dark scenes are a direct result of the fact that in the past two decades we our digital sensors got good enough to actually shoot in such low-light environments.
Before that film crews were typically shooting day-for-night which meant waiting for a set of specific weather conditions and then hoping that grading things blue-ish would sell the thing as being shot in the night.
Another aspect is the much higher brightness and contrast (=dynamic range) of today's displays and projectors. Back in the day you had to literally use the whitest white and the darkest dark available to create a readable picture (and you had to do a ton of lighting to squash the extreme dynamic range of a real world environment into the small dynamic range of your target medium). As this dynamic range became bigger it became possible to not use the whole range and still have good looking results. So in that line of thinking pictures became darker because they can be.
Not that I defend the whole thing, sometimes dark pictures with a high contrast can be good and very readable, sometimes it is used as an excuse to not do the propper work.