Because that is what the federation decided on when they established their rules.
I feel like your question is akin to asking why a football field is 100 yards instead of 98 or 102. In life, there are a million possible variables that things can or can not be. The squats could have also never been squats in the first place (which, if you look at the history of odd lifting, was very much reality), or they could have been front squats, or belt squats, or leg presses, or etc etc, but they decided on the squat without the pause.
That said, no one is stopping you from pausing your squats at a meet.