The first reason for this is that it was a huge mistake to divide Mockingjay into two parts since it didn't allow the viewers to get a complete story. On top of that, while the first movie is slow and boring, the second one feels rushed.

By the time she was allowed to return to District 12 at the end of The Hunger Games: Mockingjay – Part 2, Katniss was 18 years old.

Be prepared for intense and upsetting violence revolving around Katniss (Jennifer Lawrence) and company's revolution against the Capitol, including explosions, shoot-outs, several emotional death scenes, and one extremely tense sequence/jump-scare involving the scary creatures known as Mutts.

Meanwhile, Peeta and Katniss live in District 12 for as much of their lives as we see. The entirety of Panem is rebuilt to support each district being able to get what they need to live supported and happy lives. All in all, it's a bittersweet ending, but one that closes the door on these characters.