why deos Daisy fall short of Gatsby's dream?

To Gatsby, Daisy represents the paragon of perfection—she has the aura of charm, wealth, sophistication, grace, and aristocracy that he longed for as a child in North Dakota and that first attracted him to her. In reality, however, Daisy falls far short of Gatsby’s ideals. She is beautiful and charming, but also fickle, shallow, bored, and sardonic. Nick characterizes her as a careless person who smashes things up and then retreats behind her money. Daisy proves her real nature when she chooses Tom over Gatsby in Chapter 7, then allows Gatsby to take the blame for killing Myrtle Wilson even though she herself was driving the car. Finally, rather than attend Gatsby’s funeral, Daisy and Tom move away, leaving no forwarding address.

I'm not sure what you mean............ the relationship between Gatsby and Daisy is very innocent at this point; Gatsby is awkward with her, but there isn't any disappointment; at least not yet.