Earlier quoted context omitted.
It can ask, but how much time do you want to spend answering stuff? Such dialog is probably nice for first time user, it is a nightmare for repeated user.
What prevents the system to remember your previous choices? Then it can assume you choice haven't changed, and propose you a solution that matches your previous choices. And to give the user control it just needs to explicitly tell the user about the assumption it made. In fact, a smart enough system could even see when violating the assumptions could lead to a substantial gain and try convincing the user that it may…
Talking is not very efficient, and it's serial in fixed time. With something visual you can look at whatever you want whenever you want, at your own (irregular) pace.
You will also be able to make changes much faster. You can go to the target form element right away, and you get immediate feedback from the GUI (or from a physical control that you moved - e.g. in cars). If it's talk, you need to wait to have it said back to you - same reason as why important communication in flight control or military is always read back. Even humans misunderstand. You can't just talk-and-forget unless you accept errors.
You would need some true intelligence for just some brief spoken requests to work well enough. A (human) butler worked fine for such cases, but even then only the best made it into such high-level service positions, because it required real intelligence to know what your lord needed and wanted, and lots of time with them to gain that experience.