Here are two things I found, Not saying it's the answer but some of makes sense
In the professional game, sometimes an umpire will take a ball out of play - right after the pitch hits the dirt, so the ball has no IMMEDIATE
chance of having a foreign substance on, that is ... dirt. In addition, watch the plate umpire inspect the ball.
He's looking for any substance that might have been put on the ball by the pitcher because of the
ball's sudden drop, bite or other movement prior to diving in the dirt. Also, if a ball is "fouled" in the dirt
right in front of home plate - again, he'll inspect the ball.
If the ball is not fit for play - out it goes, usually a practice ball for the home club. BUT, if the only
thing that's on the ball is a tiny bit of soil after bouncing off the dirt, watch closely if the plate umpire
simply rubs his hands around the ball, then tucks it away in his ball bag.
When a pitch is thrown by a pitcher it has a certain spin to it. 4 seam, 2 seam, curve, whatever. When the ball hits the dirt with that certain spin it can leave marks or scuffs in the ball that may effect the way the ball reacts the next time it is thrown by the pitcher. Now when the ball is hit into play and hits the ground it has a different spin or reaction off the bat so that is why it stays in play.