Originally, local Bishops decided who was a saint and sent word around to the other Bishops for promulgation . Martyrs were a very popular choice, as were Bishops (surprise!) and of course, Popes .
By the 1000's AD, standards for sainthood among Bishops had become very lax, and several Popes decided that special councils would determine who was a saint . This didn't change anything much, but it did help lessen the number of saints until 1634, when Pope Urban VIII published a bull that made canonization and beatification exclusive to the Holy See. The Pope would appoint a special council, they would advise him and he would make a decision .
In 1969, the Roman Calendar was reformed and whilst 3 months of the year off for Saint's Days and Holy Days (holidays) was a good idea and viable in Medieval Times, it was impractical in a modern world . They had even tried to amalgamate a few with All Saint's Day, or All Hallow's Day, or Halloween . Already many saint's days were no longer celebrated, but it was made official by removing them from the calendar in order to promote more important events such as Lent, Easter and Christmas . As well as demoting saints, prominence was given to some lesser known saints in order to diversify the saints geographically and culturally so everyone could have one . Some places in the New World are still catching up to fill their quota .
Anyway, the Sainthood of many of the early saints is much suspect .
Now it must be documented after research by 3 experienced men of the church, one of whom plays the Devil's Advocate and consistently tries to disprove the Sainthood . At least 3 miracles are required .
Technically the old Saints are still there but their importance is very much downplayed by the Church because thorough research might reveal they weren't very saintly at all...most would never pass the modern criteria...best let sleeping dogs lie than attract attention to a mistake .