Well, let’s remember that Bernstein’s “Mass” was a concert piece and was never intended to be used at Mass like say one of Haydn’s Masses which were actually sung during Mass.
But the flood of music which came out in those years was astonishing. And the fact that the vast majority of that music is no longer sung is a profound testimony that maybe the rush to modernize the Church was just that - a rush. When was the last time you heard “Sons of God” or “They’ll Know We Are Christians By Our Love”? But that’s all you heard in those days. We completely abandoned our deep and profound musical heritage in favor of the new.
My mother eventually stopped going to what used to be the main “high” Mass at our parish and opted for the early Mass at 8 (without singing). She couldn’t bring herself in those days to attend the Saturday Vigil Mass (that was another change) which was the only other non-sung Mass.