I have no idea why it is not. I know my First Communion Missal says the Creed is said on Sundays and Solemnities (it is about 20 something years old), not sure what it says about the Gloria as I do not have my missal with me presently. Perhaps its a time issue, or maybe those items are considered more special for Sunday and certain feast/Holy Days.
When I go to the ExtraOrdinary Form, it depends on the feast day for the Credo (Creed) and Gloria if they are both said or not. I know it was not done at the All Souls Mass I attended in the ExtraOrdinary Form. I am sure just like the Ordinary Form, the Gloria is not done during Advent and Lent in the ExtraOrdinary Form. The Credo (Creed) is generally recited for the most part, and don’t recall a time outside of All Souls that it was not.
