The obvious reason would be that to make it work nicely as a compiler, they wanted to make it pull in files and compile them. It shouldn't be terribly difficult, though, to patch it and make it compile in-browser like CoffeeScript does with special script tags.

According to the docs it's pretty close to that already: http://lispyscript.com/docs/#browser

You'd just need to make it find the special script tags and eval them.

EDIT: Yeah actually it's already in there: https://github.com/santoshrajan/lispyscript/blob/master/src/...

Actually, it turns out it's already implemented: https://github.com/santoshrajan/lispyscript/blob/da6602126eb...

So any script with type "application/lispyscript" will automatically be parsed and run. The only requirements appear to be RequireJS and underscore.