Oliver has very beefy litigation insurance. He had to up it after the Eat Shit Bob guy sued him.
Oliver won that case.
All of his stories are researched and vetted through legal before they air. The only thing the insurance company is trying to do is chill public comment. They'll lose the court case but will cost them. We're just lucky that Oliver has the resources to mount a defense.
Anyone who says the government should be run as a business will fail at running both