After Peeta's and Katniss's victory in the 74th annual Hunger Games, they again have to face the Games.

Source: https://collider.com/the-hunger-games-movies-in-order-how-to-watch/

Katniss's defiance and escape from the Quarter Quell show the rebellion's growing support, even within the Capitol.

Source: https://collider.com/the-hunger-games-catching-fire-ending-explained/

Katniss's prickly ally in The Hunger Games doesn't participate in the final assault on the Capitol.

Source: https://www.cbr.com/hunger-games-movies-left-out-johanna-best-scene/

Knowing that losing Prim would break Katniss's spirit, Coin gave the order to kill Prim when she no longer needed Katniss to be the Mockingjay.

Source: https://www.cbr.com/hunger-games-mockingjay-glosses-over-katniss-suicide-attempt/

The overwhelming likelihood is that this is meant to be a covert way of revealing Katniss's common ancestry with the Bairds.

Source: https://screenrant.com/the-hunger-games-ballad-songbirds-snakes-family-tree-relatives/