The part I find a joke is that it's exactly what's done half a dozen times in a game - a player comes from the other side of the mark, stands short, and plays ignorant about where the actual mark is, and every other time an umpire will call out for the player to move back - except this time.
It's the same reason people thought the "dissent" call in the GWS v Blues game a joke. They let this go over and over and over, game after game, round after round, and all of a sudden pay one, often at a critical point. Yes by the letter of the law they're right but if that's the case by the letter of the law they're also wrong the other 90% of the time so the umpiring is empirically worse!
If you're going to crack down on random thing X, do it from the first bounce of the ball, pay it every time, and you'll find the players stop doing it a hell of a lot sooner than some arbitrary late game instance where you just end up looking like you've eithered up once ored up a dozen times.