For me it was just structure and ease of use. You can configure vim to make files on specific keypresses to link your diy wiki together, use gf like you mentioned to jump around, make your own auto folding and stuff...
Or you can be lazy and install a plugin that takes thirty seconds to get the hang of.
Actually writing and staying organized has been challenging due to the fact I don't focus well. Spending time recreating vimwiki is time not spent staying organized. Vimwiki has low friction so I use it.
I like the ease of use and I greatly enjoy its diary feature. This provides simple keypresses to open an entry for today or yesterday, without requiring to think about the date. It provides me quick access to make notes and continue my way. Similarly, the creating of new notes, inserting likes, and navigating these links, are made relatively easy with commands provided by vimwiki.
I suppose that it is not that difficult to recreate the basic behaviour of vimwiki with custom commands and navigating with `gf` between your notes. However, for me vimwiki provided an easy way to get started in an environment where these commands were provided out of the box. Since then, I have gotten used to, and somewhat attached, to vimwiki and have kept using it.
