Why can't they just click the undo button on whatever they did to the client?

After the patch, the client doesn't work. Like, at all. Takes 4 tries to log on, then another 4 to connect to chat. Why don't they just think, "Hey, we changed this about the client and it made it break....we should probably change it back"? I'm sure it's a lot more complicated, but this has been going on for a long while now and I personally think they could have found a solution to it.