Badlands is set in 1959 and is narrated by the impressionable 15-year-old Holly Sargis (Spacek), a teenage girl living in a dead-end South Dakota town called Fort Dupree. Holly lives with her sign painter father, although their relationship has been strained since her mother died of pneumonia some years earlier. One day she meets the 25-year-old garbage collector Kit Carruthers (Sheen). Kit is a young, troubled greaser, who resembles James Dean, an actor Holly admires. Kit charms Holly, and she slowly falls in love with him. Holly's narration, describing her adventures with Kit in romantic clichĂŠs, is juxtaposed with the gradual revelations of Kit's increasingly antisocial and violent behavior. Holly's father disapproves of the relationship between Kit and Holly, and shoots her dog as a punishment for spending time with him. Kit comes to Holly's house and shoots her father dead. They then fake suicide by burning down the house and go on the run together, making their way towards the badlands of Montana. Kit and Holly build a treehouse in a remote area and live there happily for a time, fishing and stealing chickens for food, but are eventually discovered by bounty hunters. Kit shoots the three bounty hunters dead and the couple flee. They next seek shelter with Kit's friend Cato, but when Cato attempts to deceive them and go for help, Kit shoots him, and also shoots a teenage couple who arrive to visit Cato shortly thereafter.
Kit and Holly are hunted across the Midwest by law enforcement. They stop at a rich man's mansion and take supplies, clothing and his Cadillac, but spare the lives of the man and his housemaid. Heading across Montana to Saskatchewan, the police find and pursue them. Holly, who is tired of life on the run and of her relationship with Kit, refuses to go with him and turns herself in. Kit leads the police on a car chase but is soon caught, and enjoys the attention he receives from police and reporters. They admire him and engage with him as he is sitting in their custody, asking him questions and cracking jokes. Kit is later executed for his crimes, while Holly receives probation and marries the son of her defense attorney.

Question: Why does Holly finally hand herself in to cops?
Answer: She is tired of being on the run and tired of Kit
Alternative answer: She is sick of being on the run and being with Kit.