Daisy and Gatsby come from opposite ends of the class spectrum, and to Daisy, her reputation to the upper class is the most important thing. She is constantly looking for achievements to seem worthy of envy to her ‘friends’.
Daisy chose Tom because to her he represented a secure social position and the wealth she was accustomed to. Daisy believed that Tom could make her happy because he represented things that made her happy besides love, like material things and money. But Daisy can never be happy with Tom because when she married him, she objectified him into the things he gave her; the expectations of Tom that she constructs in her head are mostly made of the gifts she has received, rather than Tom’s actual personality and morals.
