He's trading possible accent issues for me (and a lot of people) refusing to watch the video.

If your video has a robotic voice I assume it's spam, worse the voice is so annoying that I won't stay around long enough to find out otherwise.

I've started to notice a lot more videos using TTS voices for narration, presumably because the quality of said voices is increasing.

Increasing "enough" is subjective of course.

It could be that the creator doesn't feel confident recording themselves doing the voiceover, regardless of nationality.

Or they are recording the video in many different languages and it's easier/cheaper to get text translated than to find voice talent in multiple languages.