It is simple, transparent, has accumulated very large number of tools for analyzing and editing it (think of all the UNIX utilities or the complexity of IDEs).
However most of the non-plain-text methods (like UML) help you get a bird-eye view of what you are creating.
Also Humble can be embedded in rich text (like HTML) so it may have some niche uses as a real programming language.
I have built a prototype blog that you could re-program with Humble via WYSIWYG editing some time ago. It was brittle (you could break the website by errors in the main template) and slow, but it was fun to do everything in the browser.