It’s true that the Mass is a remembering of the death and resurrection of Christ. But it’s a particular kind of remembering that involves an encounter with past, present and future. In the acclamation of faith during Mass we proclaim that “Christ HAS died, Christ IS risen, Christ WILL come again.” The Greek word for this kind of remembering is “anamnesis.” It means not only a memorial, but a re-presentation. In other words, in the rite of the Mass Christ becomes “present” once again, in the here and now. In doing the actions of blessing, breaking/pouring, and sharing the bread and wine we experience once again the reality of Jesus himself. Not only did Christ die on the cross, but in the Eucharist the worshipping community dies and rises with Christ, and participates in his love-motivated sacrifice. The prayers that we pray are in the present tense because the mystery we are celebrating brings both past and future into the present with us.
I hope this helps to answer your question!