They Don’t Know What They Want or Whats Good For Them
Let’s face it, players are dumb. They get their characters thrown in jail, chased by a mob of angry townsfolk, eaten by purple worms, and mind blasted by illithids. And then they want to be rewarded with griffon mounts and rings of three wishes!
Don’t listen to their desires or wants, because they are both invalid. Design every campaign session to the letter of your vivid imagination. When your players try to deviate from your predetermined path, kindly ignore them and push them back on the railroad. If necessary, employ an army of quantum ogres.
As the DM, You Are a God
Act like it. If players give you sacrificial bags of chips and beer, they should be rewarded with your grace. If players are disagreeing with your judgement, take it out on their character without remorse.
Your players need to respect your authority, and the best way to do that is to cut off any communication with players that get out of line. If possible, convince other players to ex-communicate them as well.
Eventually they will come around to understand; and when they are begging at your feet with free pizza bites and Mountain Dew (Code Red, preferably) you can welcome them again into your loving embrace, and maybe even toss them that griffon.
The Campaign Belongs to You, and You Alone
It is important that before you start a campaign you have your players send you a list of what they want to get out of the game. Once you receive them, crumble them up and burn them while recording it. Post it on YouTube and send the share link to your players.
The key here is to make sure from the get go that your players know this is your game and your world. They are only guests.
If any of your players give you grief about this you should visit their house and begin destroying their things. They will probably ask why you did such a thing. Respond, “Now you know what it feels like to have a guest ruin your stuff.” They will get the picture and will not challenge you further.