Why is the inclusion in poetry effective?Referring to conflict.

Your question is a bit vague - but I'll answer it this way.  Without conflict, a story does not exist.  Consider the four modes of writing: narrative, descriptive, expository and persuasive.  The only one of these that tells a story is narrative.  The other three are just essays - pontifications if you will - on some subject.  And these are not necessarily for the purpose of entertaining.  More often than not, they aren't entertaining.

But narrative.  Narratives entertain.  Why is conflict necessary for a narrative?  Well, conflict is interesting period.  The entire premisis of what we humans enjoy about stories is the big problem, was it solved, and how?  This is likely because we all experience problems on a daily basis.  And in our daily lives, aren't these what make existance interesting?  Reading about other people's problems is always fun because they aren't ours - and then we make comparisons of ourselves to others and enjoy thinking, "Well, my life could be worse."