Why do authors say "have to"?

Question

I have edited many articles. It is my responsibility to try to improve the English grammar. I hope it helps.

I often see authors saying "have to" in situations where I do not see anything that is a requirement for doing. For example "In this article we have to describe" something. I do not understand why we have to describe it; we are simply describing it.

I apologize if that sounds like I am being critical. I am trying to explain what I am thinking. I really want to ask if there is something I misunderstand. I usually delete the part that says "have to" but if there is something important that is lost by deleting that then please explain.