Because it's like having a drug addict for a son. You can try and help them, but eventually it comes to a point where as much as it hurts you, you've got to cut them loose and make them learn their lessons the hard way... for the good of the rest of the family.
Essendon are the rogue druggie son that is the only one that doesn't want to abide by the rules.
Just ask Bryan Cousins...