Why would raising the US debt ceiling help the US credit ratings?

It would not help, but not raising it would hurt. The budget for the year is done, and we have incurred obligation based on the intention to borrow, If we can not borrow we can not meet all of our obligations, so some will not get paid. When you do not pay your bills, your credit rating falls. If it is interest on a bond that is not paid, the credit agencies have said they will lower the ratings on our bonds from AAA to D.