Why do Brazilians today speak primarily Portuguese whenever the
majority of the continent speaks
Spanish? *

In an attempt to stymie its rival, Spain sought support from the pope, Spanish-born Alexander VI. He created a line of demarcation to divide the nations' claims as part of the Treaty of Tordesillas in 1494. That miraculous and fateful decision is why Brazilians speak Portuguese.

Explanation:

it increase by 12% a year from 1812-1820