Take, for example, David Allen’s Getting Things Done (GTD), the life-management system that inspired many of the dedicated task management applications. The GTD system (or a variant) is medium-agnostic and can be implemented in various ways: some people implement it on a few standard index cards or in a single text file. (Follow those links to read the reasons why people use those media.) For years I’ve implemented GTD in my personal hypertext system, a set of simple rich-text HTML files written in TextEdit (a format that I described in this forum here and here). I imagine that my reasons for implementing a life-management system in my way are similar to @ryanjamurphy’s reasons for implementing a system in his way: it was the best way I could find to integrate all the aspects of my life and work. I won’t go into the detailed reasons, but that was my bottom-line conclusion.
I’ve been considering using Obsidian—all I would need to do is convert my existing files from HTML to Markdown using Pandoc, so I could very easily move my current system into Obsidian; it makes perfect sense to me, but I haven’t decided yet if the balance of pros and cons leans in that direction. My current system relies heavily on macOS tags, and I am unsure about abandoning them for Markdown tags.