NCAA actually adopted this rule about five years ago....the reason given at the time was to eliminate the "cat and mouse" games between pitcher and batter.
I later heard that the real reason is that ESPN had some significant influence after a few games in the CWS took 2 - 3 hours to play. They implied to the NCAA softball people that if they didn't want their games televised on tape delay at 3 am Sunday morning, that something needed to be done to pick up the pace of the game. The timing rule between pitches is what they came up with.
But they still refuse to implement the one minute time limit between innings....