I have a question that why all the YouTubers have this custom on their theme?
If you’re question is truly why, and not how, I reckon its one of the better way to have aa much screen estate as possible.
When shooting videoes there’s always a battle between the amount of information you want to present, and the visibility on the viewers screens. This leads to maximizing windows, and not using multi-panes unless absolutely necessary. Aka using stacked tabs in Obsidian if you want multiple notes open readily available.
I read both how and why and went with the how in the title, but it’s good to have all bases covered