This is standard behavior in pretty much any kind of art/content creation app. You have a project file which can be saved and reopened in the app, saving the state of the layers/effects/etc to be edited later, and can “export” a final render to a specific format for your medium. Image/video editing, digital audio workstations, 3D-modeling programs, they all behave like this, for good reason since it usually takes a long time to export to a specific format, and when you do, you lose the ability to change anything.

Think of it like source code, and each exportable file type is like a compilation target.