There are multiple speakers whose speech overlaps.

There is a long period of silence at the beginning of the video.

The video has poor sound quality or contains speech that YouTube doesn't recognize.

The captions aren't available yet due to processing complex audio in the video.

Well, YouTube lists these following reasons for auto captioning not being available: In fact, over half of the videos I have uploaded on to my YouTube channel aren’t able to be automatically captioned by YouTube. This might surprise you, but automatic captioning isn’t always available on YouTube. Automatic Captioning Isn’t Always Available Let’s look at why you shouldn’t be using YouTube’s automatic captioning service and what you should be using instead.

Whilst it is tempting to go the cheap and instant route by using YouTube’s automatic captioning service, there are some limitations to this service to consider. So if you are going to do it - and you should - it is worth doing it right. All of which can boost channel likes and earn you more dollars, if you are monetising your channel. Studies consistently show that adding captions increase viewership time, boost SEO, and help with accessibility.

Add automatic captions to youtube video