It's web based so no installation hassle.
It allows the raw storage of documentation.
It allows you to search uploaded documentation.
It allows you to easily search everything! At my last company, someone pointed out to me that I could find almost anything I wanted to know about existing systems in our confluence.
It is excellent for collaborative editing.
It is excellent for writing and formatting documentation that must be shared.
It has a wide variety macros and plugins that let you effortlessly embed charts and diagrams. Admittedly, some macros (ie gliffy) are vastly superior to others (lucidchart).
You can write good documentation with minimal effort. But it also provides a comprehensive set of tools to format the crap out of your documents if you want to.
At this point, I'm really struggling to figure out what someone actually wants out of a "perfect" product. A lot of the things the author complains about would require draconian solutions from a systems standpoint that would just set off another round of complaints that the system is to restrictive.