Apple’s high-level goal here should be to include responses that increase your faith in Siri’s ability to parse and respond to your question, even when that isn’t immediately possible. Google Search accomplishes this by explaining what they’re showing you, and asking you questions like “_Did you mean ‘when is the debate’?_” when they think you’ve made an error. Beyond increasing your trust in Siri, including questions like this in the responses would also generate a torrent of incredible data to help Apple tune the responses that Siri gives.
Apple has a bias towards failing silently when errors occur, which can be effective when the error rate is low. With Siri, however, this error rate is still quite high and the approach is far less appropriate. When Siri fails, there’s no path to success short of restarting and trying again (the brute force approach).
The comparison between conversational assistants and iOS’ original user interface feels particularly apt. It’d be helpful to know what else to try when Siri doesn’t understand a question.