It's a complete mystery to me why certain YouTubers do this. I'll take the worst human voice (even Fran Drescher or Rich Evans) over a synthesized one, particularly for expository narration. It reminds me of phishing phone calls, and instantly draws me away from the actual content.

A guess would be quicker production process. If you adjust the script, just rerender it and done. Actually speaking and recording takes tons of time.

I guess. But if a human can't be bothered to record it, why should I be bothered to read it?

You take back your disparaging comments against the sweet wonderful voice of Rich Evans. His angelic laugh is soothing enough to stop babies from crying.

I would guess that a lot of them are not native speakers of english?

There is nothing wrong with Rich Evans voice.

My theory is that this video was put together from footage found in another documentary (it's cropped funny like they are cropping out the original footage watermark). My next guess is the author doesn't speak English as a first language so they use a voice synth?

Sounds like he added some sort of filter on top of regular voice to sound like synthetic. It seems better than any synth I've heard. It's definitely not Amiga's translator library. :)

Kinda weird and annoying.

It's definitely synthetic. There are a few phrases which are clearly spoken other than how a human would. But yes, one of the best synths I've heard. And also very annoying.

I do believe you're right. Some weird inflections in there.