One of the perks of just-a-text-file-with-a-bunch-of-addons is that it enables progressive disclosure - it takes no learning curve to just get in and use the tool on a basic level, but additional complexity (and power) can be introduced over time.

The problem with a purpose-built app is that there's a minimum level of new concepts to learn before the tool is even minimally useful, and that's a barrier to adoption.

A good example of this in action is something like Markdown. It's just text and will show up fine without you learning anything, but as you pick up more syntax it builds on top - and if you learn some markup syntax but not others, it doesn't prevent you from using the subset you know. There is a clear path to adding new knowledge and ability.