For YT vids, especially shorts, it's because churning out shorts/reels/tiktoks of clips from longer form videos (and/or with the split screen gameplay of some mobile game/minecraft platforming run) is now a common tactic for trying to gain tons of views on your account for monetisation later.
I’ve also frequently seen it on long-form videos. I think the transcriptions must be at least partially reviewed by humans, because YouTube already has automatic transcription for videos without subtitles.
For YT vids, especially shorts, it's because churning out shorts/reels/tiktoks of clips from longer form videos (and/or with the split screen gameplay of some mobile game/minecraft platforming run) is now a common tactic for trying to gain tons of views on your account for monetisation later.