Dark theme/style was originally on mono CRTs because it gave sharper text and lower power. It went out of fashion with colour CRTs and GUI based OS.
It was resurrected for OLED, where it gives big power savings and sometimes sharper text.
It's ill-suited to LCD (needs more back-light power) and worst of all on eink, where there is zero power saving due to front light.
Also ideally you need different font hinting on dark mode, eink usually hasn't got it. It's partly fashion and encouraged by brightness being set too high on LCD backlight or eink front light.
I have the luxury of hardly ever using the front light, unless I'm out somewhere dim. I have a nice angle poise reading lamp to suit paperbacks.
But in the last years of his life my dad liked the PW3 front light for reading under the quilt.
