Religious freedom in England in the 1600s was basically not a thing, especially if the reigning monarch just happened to practice a different religion than his or her subjects.

After Queen Elizabeth I, a Protestant, died in 1603, King James I, also a Protestant, ascended the throne. Guy Fawkes was a devout Catholic. Given that English subjects couldn’t whine about their ruler on social media back then, Guy Fawkes was like, “I’ll get rid of James so a Catholic can rule England.”

Source: https://www.distractify.com/p/why-is-guy-fawkes-day-celebrated