I'm on the spectrum. I can process reading way, WAY faster than I can process someone just audibly speaking to me. That shit's actually helpful. I admit, it doesn't need to be in the center of the video though.
So who is it for? This is everywhere. It's in YT shorts, Instagram posts, etc. As a style, it's getting pretty ubiquitous, and I don't understand the reason for it. At best it's annoying because if I look away for a split second, I'll miss a couple words and it won't make sense anymore.
The one word at a time thing is a way to demand more of your attention. It's just a side path of the old advertising stick where words would 'pop' in weird ways. See this video for an example.
I don’t understand it either but it’s a product of how people consume the videos in their upright depression rectangles in public places with no volume I’d imagine.