Because the Dems need the optics of all white old men, (mean Rep), asking tough question and for the Dems to be able to interrupt the questioning with loud condemnations of “how dare you”, “you are out of line”, “this is bullying”, “we must adjourn immediately” etc. That is why the don’t want a prosecutor to question her, it doesn’t allow for those type of theatrics.
All hey need is one soundbite, a tearful “Brett Cavanaugh tried to rape me!”