The reason they make you go through the state doing an amended after you amend the federal is because the federal and state returns must match. The two government entities share information that is in your return to be sure they match.
If you have a state return in TurboTax along with the federal, then they have to make the assumption that both were filed with the numbers in them.
If you are changing the federal return by amending, then the state return will also need to be changed to match and file.
If the state return was not in TurboTax to begin with, then they would not see a need to causing you to amend the state return when you amend the federal return.
