Cause it's kind of a confusing rule, and I don't blame Drew at all for wanting to simplify his description. He usually does allude to it though.
Even when Bob did it, he explained that you could play the ace later, but even for years and years it never entered into my mind why anybody would want to play it later.
Bob, it seemed, preferred contestants using the ace right away, and this could lead to some issues with the game. I'm reminded of the
January 17, 2007, playing of Card Game. A contestant drew an ace and Bob urged her to make a final bid for the car. However, the contestant was unsure what to bring her bid to, so she put it aside. Bob questioned why she wanted to do that since she could end the game right there with a final bid for the car. Eventually, Bob let the contestant hold the ace.
Later on, Bob reminded the contestant she had the ace to use, so she set a bid for the car. However, she immediately wanted to increase her bid a little more, but Bob effectively told her she finished bidding (even though she was allowed continue drawing). The contestant lost by $5, and many of us wondered how the show continued without acknowledging Bob's mistake and giving the contestant the car.
Unless I'm mistaken, by the time Card Game's current set came out, the "hold the ace" rule was dropped; contestants are now forced to give a final bid or a positive dollar amount for the ace.