The Church has softened its language. The people who invented protestantism (Luther, Calvin, Zwingli, etc) were all Catholic, as well as the large majority of their early followers. (Luther was an Augustinian priest; Calvin had seriously considered a religious vocation, and some claim that Zwingli spent time as a Dominican novice.) The leaders of this new movement could rightly be called heretics, because they were Catholics who were teaching contrary to Church doctrine.
But modern protestant leaders and teachers are usually not Catholics. They cannot rightly be called heretics, because you have to be a Catholic to be a heretic (at least as far as the Catholic Church is concerned).
Furthermore, in modern parlance, “heretic” is considered an insulting and pejorative term, and the Church has no desire to insult protestants (only to correct them and lead them closer to Jesus).