The act of writing code that solves challenges is what makes one a software engineer (at the barest minimum). As challenging as writing code is, it's somewhat ironic that software engineers prefer to write code than write about the code they've written. Documentation is one chore that software engineers aren't very fond of.
There's so much paperwork involved in the process of developing software solutions, you find that a lot of software engineers would rather write programming languages than write normal words understood by people. It's largely because these documentation are about making sure the solution being developed follows structural processes and helps the final consumer understand what was developed, why it was developed and how it should be used. Of course there's more technical documentation on the technology used and other esoteric details, all in all, some people find it baffling that a software engineer will pick writing code (which is somewhat difficult) over stringing sentences together that's easily understood by the average person.
Documentation is quite important especially with the technology as different versions of software solutions are deployed frequently, it is very crucial that one can understand what each version does and its limitations. You find that even programming languages have their documentation, it's a document that explains the rudiments of the programming language and is more or less the Bible for said programming language.