Slide advancing is turned off because if it were left on, clicking anywhere on a quiz question would advance the slide to the next slide without evaluating if they choose the correct answer or not, and also the TRY AGAIN/Back buttons would not function properly.
Essentially, what you would need to do is add an active area on each slide that advances to the next slide.
You can of course turn on the advancing if you dont mind the above consequences.
To do so go to:
SLIDE SHOW > SETUP SLIDE SHOW > SHOW TYPE = PRESENTED BY SPEAKER