Earlier quoted context omitted.
While I agree with you that the homepage doesn't do a good job explaining what Circle CI is to someone unfamiliar with CI, your criticism of the video doesn't make much sense to me. The video has a voice-over explaining what Circle CI does, and includes subtitles for when you don't have sound.
That's true. But if all the information is contained in the text. Why not make it a text I can read at my own pace instead of forcing me to watch it through a video at no additional benefit.
So I guess they wanted a YouTube add, so it needed video and once they had paid to make that said hey why not stick it on our homepage? Or something like that.
It could have also gone the other way: as a useful video describing how things works, and then it got a second life as an ad - but the former path seems more likely.
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[1] I'm not sure why they are targeting me so heavily, but I see this ad more than any other, by a large margin.