Brazilian Catholic christianon here. Protestantism was rapidly growing here in the 1990s and 2000s for a variety of reasons
-People here are veryimpressionable by prosperity gospel, speaking in tongues, religious cures and other stuff promoted by our prot churches. Some people are also turned away by the Church's doctrine on divorce and contraception.
-It's very easy to open a protestant nondenominational church, especially in poor areas (favelas), and a lot of people just go to the nearest church to their homes.
-Part of the Brazilian Catholic hierarchy was way more interested in promoting "social justice" and socialism instead of preaching the gospel and fighting the prot wave.
-Prots have a shitload of TV and radio stations, so they spread their message way faster and more efficiently than Catholics
-Prots here control a big number of political parties, and a lot of preachers run for office and gain political power (see Rio's mayor), which is then used to further their own denominations.
-As previously stated, the Catholic hierarchy used to support the commie party, that didn't give a damn about religion. Protestants also supported commies, but they demanded more political power in return, and the commies obliged.
-I'm sure there are many other reasons.
Bear in mind that "mainstream denominations" (Episcopalian, Presbyterian, Methodist, etc) form less than 10% of our protestants. Most of our pastors are megachurch Joel Osteen types. Pic related is the Temple of Salomon, a huge Temple of Jerusalem replica in the heart of São Paulo. It was built by Edir Macedo, who controls the biggest protestant denomination in Brazil.