I think it's mainly in relation to the constraints of the game engine, and also that the game engine being flexible enough to enable the gimmicks. I haven't played DDLC and probably never will, but from what I've read about it, like games with similar core themes (not dating sim) it has some gimmicks that tend to stretch the capabilities of a closed-down game engine, sometimes requiring patches to the engine itself. In this case the game engine Renpy offers an extensive DSL that makes it easy to add story scenes, media and dialogues, but allows you to fall back to python to do some tricky things.