ok, then i understand your reasoning.
i can see (no pun intended) how people with certain eye conditions like astigmatism might want to keep total light emissions around them minimal. according to some reports darker backgrounds helps them read.
personally i use white backgrounds and black text and my screens are old, meaning they don't have an overly high brightness and contrast.
in general contrast effects readability. you can easily convince yourself of this fact by looking at the two extremes. infinite contrast would mean white is blinding bright, even for my liking
meanwhile zero contrast leads to one solid color with no visible text.
the sweet spot in the middle differs between different people.
from an information theoretic point of view, i would try to retain the maximum signal level till the last step before reaching the observer.
with black on white or white on black text, the user can personalize the experience via e.g. brightness/color balance/contrast knobs on the monitor.
reducing the contrast or inverting the colors is always easy as a last step, while first decreasing and then increasing the contrast is not possible without losing information, so i don't like it.
when i stumble over websites that create eye cancer like the one you linked to I resort to the "reader mode", i.e. this is how i would observe that site you sent:
http://176.31.253.70/screenies/2018-08-07_15.28.02.994220445.pngbtw, my favourite terminal is provided by the rio window manager in plan9, incidentally it has a white background color.