A lot of people are coming up with different theories. I have tried mentioning some keywords in my videos and I didn't get me anywhere neither did it get any sales. Maybe it works for big influencers friends with sophisticated equipment and good internet but for upcoming content creator like me, voice recognition is still struggling as it finds it difficult to understand my accent. What I do is just put the keywords in the caption and text overlay, that one works better than shouting keywords at the top of my voice. 
