Because it gives some history of religious beliefs and practices. In particular, it shows that many of the ideas from the New Testament that we often think died out with Catholicism only to reappear in the late 1700s actually continued to exist. It also shows that despite what Roman Catholics would like to think, they did not have a lock on religious thought and practice, even during their "hey-day."
I use it as a partial illustration that what Jesus stated was true: his kingdom never ends. It is impossible to squash true Christianity because someone will read the Bible, see for themselves what is required, and start it once again in their area. John Hus had flaws. He made mistakes. But he saw more of the truth than many people in his day.
There are several articles about the history of the church and denominations since its foundation on this site. See:Church History