I remember when the first CRT monitors were around, the brightness was not enough, and it was considered normal to make a bright background to improve the contrast of the text. But now, when LCD monitors are very bright, it is harmful to make the entire screen bright.
I will make a tour into history to better understand the question. In 1990, I had a ZX Spectrum computer. It was called that because it was color, and the previous model was black and white. The computer had 8 colors, and also had a high-brightness mode, which gave 8 more colors. This palette was similar to GCI and used 4-bit RGBI palette.
You can find the CGI palette and it says that white (also called light gray) has the code #AAAAAA , and high-brightness white (HI) has the code #FFFFFF .
If you look at the source code of a web page, many sites have a background with the code #FFFFFF , that is, high brightness. In fact, the background color code should be #AAAAAA .
I propose to organize a community to explain to page authors that they cannot use the color #FFFFFF as a background, and to reduce the relevance of bright pages to search engines.
Black and white may be jarring, but it's easier to turn down the brightness than to have to use a custom stylesheet just to make grey-on-grey more readable.