It's a throw back to the "good old days" when all seater stadiums were less common.

The player running towards the crowd would cause a surge forward of fans.

Ok for the big and fit but a problem for the kids and elderly that might be at the front.

The bigger issue here though is how thick the players are, they know the rule but they still do it. Ditto the taking off of shirts.

Make the offence an automatic red card and the problem would disappear.