Interesting question. I think the answer lies in who the audience and what the purpose for the writing is. If research based for an academic audience, then the preference may be a systematic approach. If a business audience, the reader wants to find the info quickly (systematic/use of headings). If a more general audience, narrative works very well as it is more understandable for many readers. But, I have seen some very well written 'blending' of the two approaches, as some information must be presented as narrative to truly capture the full meaning. Hope this helps and prompts responses. :-)
Good response by Gloria. Anees, in my mind, a common reason would be it is 'easier' to perform a narrative review. This may be appealing for many reasons, time constraints, reason for review i.e. Honours Degree, single authors etc. Being 'easier' may also appeal to those that do not want to be 'constrained' by the systematic and linear process that underpins a systematic/integrative review - to 'talk more broadly' on what the literature is reporting - as well as the literature doesn't have to be primary research.