Some part of this is due to a growth in other religions caused by immigration and their differential birth rates but the real cause is Christians no longer believing in Christianity.
This is mirrored across the Western world:
quote:While most countries in the Western world were historically almost exclusively Christian, the post-World War II era has seen developed countries with modern, secular educational facilities shifting towards post-Christian, secular, globalized, multicultural and multifaith societies. While Christianity is currently the predominant religion in Latin America, Europe, Canada and the United States, the religion is declining in many of these areas, including Western Europe, some countries of North America (including the United States), and some countries in Oceania. A decline in Christianity among countries in Latin America's Southern Cone (in particular Chile and Uraguay) has also contributed to a rise in irreligion in Latin America.