Like any adaptation, The Hunger Games movies couldn't include every detail from the source material. Sometimes, entire characters and plot lines must be removed for the sake of time, such as the true origin of the Mockingjay pin and Haymitch's backstory in the second Quarter Quell. Other parts of the story simply aren't as fleshed out as they are in the books, like Katniss and Peeta's history before the Games. One such detail that wasn't fully explained in the films was the tesserae.
Source：https://www.cbr.com/hunger-games-tesserae-explained/
