Which situation was a major contributor to the Protestant reformation?

The main driver for the Protestant Reformation was the Catholic Church's self-created practice of selling indulgences.

The sale of indulgences is not something that is ordained in the Bible but the Catholic Church over time developed a system where you could, in essence, bribe your way into heaven.

For many strict Christians, this was a bridge too far. They wanted the Church to limit itself to the teachings in the Bible.