Because hardly anybody understands it at all. So all that wonderful theology and miraculous economy of expression in the ancient collects and orations (such of them as survive) goes clean over the heads of generation after generation of Catholics. Instead of being immersed in Liturgical prayer, the prayer of the Church, they have to get it in second-hand formulations called "catechesis". The results are all around you.
wherein the logic of the NOM in Latin?
Because the "laity" are too dumb to learn Latin. Didn't you know?