Google recently changed the call screening behavior. There is no longer a user-controlled setting to ask, or not ask, for the caller's name. Now, if you have call screening enabled, and the caller's number is in your Google Contacts, it will bypass asking for the name, and if the caller's number is not in your Google Contacts, it will ask them to say their name. It will ask the caller every time they call, unless you add them to your contacts.
The Goog works in mysterious ways. If you don't like this new behavior, then feel free to submit feedback on the Google Voice web or mobile user interfaces, by clicking the feedback link.