The league uses very minor little rule tweaks like this to emphasize scoring in games. This rule has just the tiniest effect in making sure DBs stay a few more inches off of a receiver as they race downfield.
And my guess is that while a ball thrown in the air for the receiver, while both the receiver and db have exactly equal right to go up for the ball, if both do go up for the ball equally but the receiver nudges the db first he is less likely to get called for offensive pass interference than the db doing the same type of nudging.
Hey I get it, the receiver is like in baseball with the hitter going to first on a ground ball, if the throw to first is basically there when the batter is hitting first base with their foot and it’s a total crapshoot as to if the batter is out at first or not, time goes to the runner as they say and he’s safe. Same thing. The offensive guy gets the better of most calls in both football and baseball.