Sometimes it's actually better with dark background on direct sun.
If we are talking about devices screen, white background kinda goes yellow on direct sun and contrast reduces. But black background goes dark grey and less light gets reelected back to the eyes.
If we are talking old school paper ( SHOCKING i know ). It's close to unreadable on direct sun when paper is white because it shines back too bright, it hurts eyes but black paper it much more comfy on eyes.
Note: Reason why black on white was used historicaly is most likely economical. (Less paint, easy to maintain.) If papyrus naturally turned black, all written text might have been in "dark mode" from the beginning.
It doesn't seem to be the case with distros like Mint. I even know folks who have Mint but they have no clue about tech or computers at all. As users they can hardly tell difference. And It's actually easier on them because it doesn't get all messy as Windows does for non tech folks, so there is almost no maintenance needed. I very much recommended it for granparents and such, so you don't have to go fixing their Windows PC each visit because they downloaded tons of random danger ware by not understanding what they do.