Forced-choice is deliberate because it maximizes the information of the question. If you put in intermediate options, that can mask real differences by letting peoples' differing preferences for certainty influence whether their responses are informative or not. (People have information or preferences they don't even realize they have, like in some perceptual tasks, and you can't detect this without something like a forced-choice because if you give subjects any other options, they'll just say they don't know.)