What could I watch on YouTube with my mother?

Hello,

a question we discussed and could not find a solution for:

YouTubers ask viewers to do the usual “Like, Subscribe and Comment” because YouTube needs them. However, some people often say that you should watch the video until the end or that they put the most important things at the end so that the viewers stay listening.

Why do YouTubers say that? What is the point of watching the videos to the end? Does it have something to do with the fact that they only get paid when the videos are watched completely or is that affected by the algorithm or something? Isn’t it enough that the videos get clicked in the first place?

Are there completely different explanations for this?

Maybe someone knows. Thank you!