Why is "All that remains" banned from Android: Netrunner World Championships?
There is nothing banned in All That Remains.

This exception was added in the update to the Tournament Rules for the World Championship to clarify that because it was being released so close to the Championship, it would not be legal (since players would not be able to adequately play with it first).

I expect this exception to be removed in the next update now that the World Championship has concluded.