> Save energy
Only on one type of oled? It's more energy intensive than white on the majority of screen types.
> Stealth mode / Meditation / Better than standby mode
This might blow your mind but... phones can be placed face down. Or hit the standby switch. Or put it in your pocket. All way easier than going to your browser, finding it in bookmarks, and selecting black.
Monitors have an off switch you can just reach over to, that is also way easier.
Additionally, both of these methods _actually_ save energy.
The reasoning is super flawed but I'm glad you probably had fun writing it. That's all that matters.