Hola uds. This was confusing to me also. I asked my wife. It was kind of humorous watching her run the phrasing through her mind. Here's what I noticed that helped her work it out. It's not that por was added. It's that que was replaced with por qué. Notice the tilde. Then she rephrased the sentence to No tienes razón para ponerte tan político.
This makes the given translation a little misleading, although not incorrect, as it's really more about not having reason or sufficient cause instead of meaning having to.
My wife said that using the por qué or razón para phrasing emphasizes a little more the motive behind the action and in it's negative form, as this example, is used often in given correction.
You don't have any reason to get mad.
No tienes por qué (razón para) enojarte.
Hope this helps.
As far as level goes, I'm still in level two and haven't completed a lesson since my wedding. lol