Nick asks himself this question early in the novel. Invited to dinner by Tom and Daisy, he learns that Tom is having an affair and that Daisy knows it and is unhappy about it. Nick finds himself unimpressed with Tom, his very wealthy but racist and small-minded former college friend. Driving home, Nick wonders why Daisy stays with such a mean, philandering man:

It seemed to me that the thing for Daisy to do was to rush out of the house, child in arms—but apparently there were no such intentions in her head.

This foreshadows the fact that Daisy won't leave Tom even when Gatsby offers her an out that would allow her the wealthy lifestyle she is used to.

Daisy stays because over the five years of their marriage, she and Tom have developed a bond, even if their marriage has been dysfunctional from the start. They have a child together, and they have grown, in their own way, to love and depend on each other. Daisy makes a psychodrama out of Tom's cheating—at the first dinner, Nick is uncomfortable because he senses that Daisy is striking a phony pose to elicit from him a "compensatory" emotion—but it is clear that she has accepted that there will be an endless string of flings with lower-class women.

Nick catches a glimpse of their relationship as he watches them seeming to conspire after Myrtle's death over cold chicken in the kitchen of their grand house. He sees that they understand each other. Further, Tom offers Daisy wealth, protection, love (in his own twisted way), and a position at the pinnacle of the class structure, none of which she is about to abandon.

One has to understand that Daisy is quite a shallow individual. She's grown accustomed to leading a life of wealth and ease, so she's understandably reluctant to leave Tom, thus potentially putting her luxurious lifestyle at risk. Daisy knows full well what kind of man Tom is, but she's prepared to overlook his many indiscretions for the sake of the stability that married life brings to her.

But this raises the question: if Daisy cares so much about wealth and glamor, why doesn't she leave Tom and marry Gatsby instead? The answer to this question is that, in addition to craving a luxury lifestyle, Daisy is deeply class-conscious. Sure, Gatsby may be loaded, but he's "new money," just one of the many parvenus residing in West Egg. Daisy, on the other hand, is "old money," a member of the East Egg social elite. Thus, the two would-be lovebirds have no future together.

Even in an increasingly materialistic age, blood still counts for something. Daisy may be dazzled by the opulent glamor of Gatsby's parties—she may cry over the immaculate tailoring of his expensive shirts—but there's one thing that Gatsby's phenomenal wealth will never be able to buy him, and that's a pedigree. This is something that Tom Buchanan will always have, irrespective of his deplorable behavior and thuggish personality.

Despite the fact that Daisy is unhappily married, she is content knowing that her wealth is secure. Daisy is portrayed as an extremely superficial, materialistic woman who is solely concerned with maintaining her wealth and upper-class social status. Daisy hails from a wealthy family and is attracted to Tom's social status. The day before their wedding, Tom even gave Daisy a pearl necklace valued at $350,000 ($4.7 million in today's currency) as a gift. Although Daisy is discontent with her marriage to a morally debased, selfish man who continually cheats on her, she is able to overlook Tom's discretions because of her comfortable, rich lifestyle. She even begins to carry on an affair with Jay Gatsby while Tom is seeing Myrtle Wilson. Despite having feelings for Jay Gatsby, Daisy acknowledges that there were times that she loved Tom, and she is not willing to leave her secure life of luxury for a bootlegger. In the end, Daisy views Jay Gatsby as a risk and would rather stay with Tom because his wealth is secure. Daisy is also an immoral individual and has no qualms about cheating on Tom (as he does to her).

Daisy may not love Tom all the time, in all situations and circumstances, but she does love him at times and she certainly loves the lifestyle his money allows her to have.

Daisy and Tom have apparently developed a relationship of coexistence that serves both of them in an advantageous manner. They each have their lover (Daisy with Gatsby, Tom with Myrtle) for excitement and passion; they have each other for social respectability - remember, divorce wasn't nearly as accepted in the 1920's as it is now - and for some measure of stability. There is comfort in familiarity, and they have found that situation. When Nick sees them through the window late in the evening of the accident,

Daisy and Tom were sitting opposite each other at the kitchen table...He was talking intently across the table at her, and in his earnestness his hand had fallen upon and covered her own. Once in a while she looked up at him and nodded in agreement. They weren't happy...and yet they weren't unhappy either. There was an unmistakable air of natural intimacy about the picture, and anybody would have said that they were conspiring together.

The conspiracy being developed, it would seem, was the plan to cut their connections with that place and those people, to flee the scene of Daisy's indiscretion and find another place to continue their self-centered lives.

They were careless people, Tom and Daisy-they smashed up things and creatures and then retreated back into their money or their vast carelessness, or whatever it was that kept them together, and let other people clean up the mess they had made...