The custom of Gregorian Masses still exists. Even before Gregory the Great (pope from 590 to 604), some people or groups would have Mass celebrated on 30 consecutive days for a person who had died. After Gregory, it became popular in Europe to have 30 consecutive Masses said for others who had died.
While the custom has been approved by Church authorities, and confidence in it called pious and reasonable, there can be no guarantee of its efficacy. The deliverance of the departed depends on God’s mercy and pleasure.
I believe priests do not speak much of Gregorian Masses for several reasons. The custom does not pertain to the essence of faith but rather depends on private revelations. Further, it is very difficult for most priests to fulfill the requirement of celebrating Masses 30 consecutive days for the same intention.