Strangely, the same can be true for plain old fashioned paper. The other day I was outside and had to look at a paper. Plain, white printed paper with black text. The bright hot sun reflected off of the paper and I couldn't see anything. A darker shaded advertisement however was easy to read.
So it's all relative. In my case I just prefer not to feel bright light blinding me, so I spend most of my time in dark mode editors/etc. My biggest complaint is that websites don't let me choose. I really wish OSs would start enforcing full dark or light modes as an accessibility feature. As I wright this, my HN screen is quite bright. I frequently flip between my dark editor and my bright Slack work screen. Those bright flips kill me.