Why do we not say the Creed and Gloria at the daily mass?
The reason is what we call the hierarchy of celebrations. Just as a 25th wedding anniversary typically is more of a celebration that the 23rd anniversary, so too the liturgical year has days that have greater solemnity. It doesn’t mean that any given mass is less than another; it just means certain ones celebrate something of more significance than others. Our highest or most solemn celebration is Easter, followed by Christmas. From there we go to regular solemnities, of which Sunday is always a solemnity. Going down the ladder we then have Feast days, obligatory memorials, optional memorials, and filial or ordinary days.
Typically on Feast days the Gloria is added to the mass and on Solemnities the Gloria and the Creed are both added. In addition on weekdays normally there is only the first reading and the psalm before the Gospel, while on Feast days and Solemnities there are two readings plus the psalm before the Gospel. So like anniversaries, while all are of value and best not forgotten, some of the Church’s celebrations have greater significance or solemnity.