During the revisions of the Missal after Vatican II, it was decided to expand from a one-year cycle of readings to a three-year cycle for Sundays and holy days and two-year cycle for weekdays. A complete breakdown of the percentage of the Bible that gets read at Mass under the old and the new lectionaries is here; the bottom line is that if you went to every Mass for three years, you would hear 13.5% of the verses of the Old Testament (not counting the Psalms), versus 1.0% under the old lectionary, and of the New Testament you would hear 71.5%, including 89.0% of the Gospels, versus 16.5% of the NT and 22.4% of the Gospels under the old system.
The new lectionary was so successful that a number of Protestant groups subsequently adopted it, but it is Catholic in nature.