The simple answer to "why not run this in a web page?" is that I built this tool based on my own needs and I never had any need to run a file system-based tool in my browser.

On the other hand, if I wanted to ship something similar with a built-in editing experience, then I think running it in the browser would be the way to go. The problem I saw there (last time I checked) was that I couldn't write directories of files to the file system from a web page (and I definitely want to store everything in the file system).