That's because every ref's word is final. That's the way the game is run. Most of the game is just a judgement call. Is it a penalty, is it not a penalty? The only person who can decide is the Ref.
And unlike REAL Football, the play isn't constantly stopping. The ref can't stop the play of the game to make sure his decision was right, or stop it to see if anything happened.
That being said, I would like a modified replay system being used. It wouldn't be used in the game, but out of it and afterwards. The entire system is in such shambles that 75% of the time when a player goes to the ground, it is a dive. A dive, even for the most minor of bumps is a yellow card.
So the system would be used. Afterwards, the game is reviewed. Any player who commits a dive, whether or not a penalty is called, is suspended for 5 games.
Maybe, just maybe, then the game will actually turn into a real man's game. Where the players push hard, hit hard, and only go down when they ARE REALLY FOULED. No more of this pansy pansy european bull****.