“Mysterium Fidei”

Why does the Traditional Canon “insert” into the pure Gospels words not uttered by Christ, namely “The Mystery of Faith”?

Such is a question that some ask. A pope has already answered.

1. The Gospels are not exhaustive reports of what Jesus said. Obviously.

2. “We believe that the apostles have received from Christ the words of the formula found in the canon, and their successors have received them from the apostles.” Denzinger-S #783 (Fastiggi translation).

The more pertinent question is why these words are not in the present canon and Eucharistic prayers of the Novus Ordo. Trent affirmed the importance of these terms in its decree on the Mass. It seems to me that if the current prayers were reformulated, reflection on this question would be very important.