That "Close Out Cover" will deflect branches, brush , keep mud from flinging forward, and most importantly, deflect any hapless Pedestrians body parts from being entagled in the rotating wheel.
Form Follows Function.
Buddy of mine has current JK Rub that he watch a large rock that was kicked up from drivers tire go through this space between finder and bumper, bounce off dirt road and hit his windshield! He had to tell insurance that his own vehicle threw a rock and hit his windshield. LOL