The problem is like @RobinsonX says, making 3D games is more difficult. A lot of users don't consider the extra difficulty that comes with creating 3D games.
Creating 3D models, animations, etc. Is just more challenging and resource intensive than 2D sprites. With 2D games anyone can do it, you don't need any special tools. AND, getting 2D art online is much easier since there is a pretty standard graphic format. With 3D content there is no standard, so you're going to have a hard time finding assets that work with out more specialized tools.

Unless we change it completely like some of the platforms you mention, where you are limited to what you create. In those platforms you're essentially working with their templates and changing some basic settings around. You don't have the full creative freedom that hyperPad provides.

You can take a look at HypeHype for example, a 3D game building app on mobile, the user interface was extremely cluttered and you were very limited in what you can do - customizability was sacrificed for performance.