While you cannot hide all of the channels you see on Apple TV's home screen, you can make most of them disappear.  I'm sure youu have no need for the Tennis Channel, Crunchy Roll, or others. You might not even need the YouTube channel because you can AirPlay that content from an iPad or directly from your Mac.

To accomplish this on your Apple TV, go to Settings>Choose Main Menu.  Change each channel from Show to Hide that you deem necessary.