Jack Straw serves as a literary prequel to Shakespeare's Richard II. The events of Jack Straw take place in the early years of Richard II's reign, and lay the foundation for the events Shakespeare depicts in that king's eponymous play. In Jack Straw we see Richard II, little more than a child, and hopelessly overwhelmed by the concept and the practical requirements of kingship: he would rather be praying than ruling. Richard blushes at the thought of his subjects dealing with him so rudely and brazenly, but he is also squeamish about punishing them. Richard is so out of his element here that his mother comes to the site of the rebellion to advise him.
Richard II's incompetence is on display in Shakespeare's play, but Jack Straw gives us the chance to see the foundation for the Richard's deposition. Where Shakespeare gives us a glimpse of Richard's inefficacy in Richard II; Jack Straw more completely paints a portrait of events that plunged England into 80 years of civil war. And that is a portrait that was especially important in the early 1590s: the royal succession was doubtful, and Elizabeth I was gaining in years. Elizabeth's military campaigns in France and the Nine Years' War was just beginning in Ireland, and a new generation of leaders were governing on the privy council, and Elizabeth increasingly relied on spies and propaganda to maintain the illusion of peaceful and stable governance.
In 1593 (or 4), Jack Straw wouldn't have just been a literary prequel to the Shakespeare's English histories, it was also a plea to prevent history from repeating itself. Given that Shakespeare was himself writing his earlier English histories at that time, he seems to have had similar concerns.