Why were there so few priests in each city?

In the years since World War II there has been a substantial reduction in the number of priests per capita in the Catholic Church, a phenomenon considered by many to constitute a "shortage" in the number of priests. From 1980 to 2012, the ratio of Catholics per priest increased globally, with the number of Catholics per priest going from 1,895 to 3,126."[1]

In 2014, 49,153 parishes in the world had no resident priest pastor.[2] Between 1970 and 2017, the number of priests declined from 419,728 to 414,582 in 2017.[2][3]