Keep their attention
I have been doing Youtube since 2012 and a lot has changed. One change that happened is that if you get more watch time on your videos more people will find your video. It used to be the most views on the video but having a lot of views might also help watch time go up too. Likes, there is a reason why some people ask for likes on their video because that is the best engagement button there is on YouTube better than comment even.