I’m new to Instructional Designing and I have this one question—

Rise is a form-based program, that is, the main programming is already done, and the developer just has to add their text and images. That makes it easier to use—and easier to provide as cloud-based software. 

Storyline gives the developer a lot more control over what happens and when. In other words, using it requires more than filling in the blanks for pre-designed blocks. That requires more complicated programming. I doubt that Articulate would want to put in the effort to create a cloud-based version. In fact, I'm not sure that would even be possible.