I was thinking the same exact thing! Except he had no choice since CNN predicted this kind of thing based on the disaster that was the last debate and the brutal Trump interruptions and talking over Biden that they automatically cut off each candidate's microphone as soon as their time was up LOL! Brilliant, and it worked.
In the end, it didn't matter how much CNN stacked the deck in favour of their man. What they didn't - and couldn't - allow for, was the 'Biden Factor' - the one thing that draws viewers more than any other, watching a car-crash in real time. Trump didn't have to say a word, and his polling would have increased. Which it did.