Because all she truly cares about is money. Gatsby doesn't have enough money for her taste so she chooses someone who does. Really, in my opinion, the character of Daisy was based on Zelda who, as you probably know, broke off her engagement to Fitzgerald b/c he "didn't have enough money". So restating what I said she left Gatsby b/c she wanted money. Her and Tom were perfect for each other b/c they are both corrupt and heartless.
Daisy doesnt want Gatsby anymore
Daisy broke her promise to wait for Gatsby and not marry Tom Buchanan. Despite telling Gatsby she would ultimately choose him, Daisy went through with her marriage to Tom, betraying Gatsby's trust and hopes for a future together.
That she will always love Gatsby, no matter what.
Gatsby asked Daisy to look at the green light across the bay, symbolizing his hope and dreams for their relationship.
She feels as if she is too good for everyone at the party, so she is very temted to leave, but she doesnt want to leave Gatsby, because she likes him.
Nick tells Gatsby, "Go to Atlantic City for a week, or up to Montreal." Gatsby would not leave Daisy until he knew what she was going to do.
Daisy and Gatsby first meet in "The Great Gatsby" at a party in Louisville in 1917. Gatsby was an officer stationed near Daisy's home, and they fell in love during this time.
Daisy
The Buchanan's are Jay Gatsby's neighbors. Daisy Buchanan had fallen in love and promised to wait for Gatsby while he was at war. However instead of waiting she married the wealthy Tom Buchanan.
Daisy does very little in The Great Gatsby. She is shown to be defined and manipulated by the men which surround her. Daisy is married to Tom, they are wealthy and represent old money within the book. Daisy has a child which is treated as a possession and used in the novel as a conversation starter. Daisy is torn between her husband, Tom, and Gatsby. Before her marriage, she was loved by Gatsby, whom she pledged to wait for, while Gatsby gathered a fortune so that he would be a suitable husband. However, Daisy was unable to wait for Gatsby, another example of her lack of power, and married Tom. Daisy is unable to choose between her two lovers, and instead allows herself to be dominated by Tom, who takes her away from Gatsby at the end of the novel.
Nick learns that Gatsby isn't what people have said him to be. Gatsby served in the war and studied at Oxford. At first, Nick is skepitcal about what he says because the way Gatsby is speaking seems akward and suspicious to him. But Gatsby senses this tension and pulls out his medal from the war and a picture of himself on the polo team of Oxford.
In Chapter 7 of "The Great Gatsby," Myrtle is killed in a hit-and-run accident by Daisy Buchanan, driving Gatsby's car. Daisy was driving recklessly while trying to escape a confrontation with Tom Buchanan. Myrtle runs onto the road, and Daisy accidentally hits her without stopping.