Your comment would be more useful if you gave us that reason.
"Filesystem as the API" in this case looks more like "convention over configuration" (which has worked fine for other frameworks like Rails), it doesn't actually seem to be using the filesystem as the only storage backend.
Ah, I see what you're saying. I didn't consider deeper/complex routes with parameters.
This scheme seems to force route parameters into query parameters. Disadvantage: It's not RESTful. Advantage: Your route parameters are now named query parameters. You only handle one dict of parameters...
"Filesystem as the API" in this case looks more like "convention over configuration" (which has worked fine for other frameworks like Rails), it doesn't actually seem to be using the filesystem as the only storage backend.