Because that wouldn’t help. You’d give them half the distance and another shot. Eventually they might score.
This trick only works when you are the offense, trying to run out the clock. If you can afford a 10-yard holding penalty, you can trade that 10 yards for the extra 5-10 seconds you get off the clock.
And in this case, it was a 4th-down play where they were giving up a safety anyway. A holding penalty would have resulted in a safety, which is what they were getting anyway. So by holding, they just allowed more seconds to run off the clock.
(I’d have to check the rule book to see if, because it was a safety anyway, the defensive team had the choice of taking the penalty on the ensuing kickoff, but even that would just mean 10 yards on a kick).
And they’re discussing Frank Gore’s junk over here:
http://www.freerepublic.com/focus/f-chat/2985025/posts