Pairing off was pretty much the norm in the 1920s. Jordan is a golfer, she is of a relatively upper-middle class (although her lineage is not specified) - she is not quite as much of the elite as Tom and Daisy, but she has associated herself with the elite and made herself comfortable in those circles. As such, she is at the right level of society to make a good partner for Nick. Daisy and Tom are firmly entrenched in the idea of what is socially acceptable. Jordan would be socially acceptable for Nick, and it would give them a balanced group. At the start, Jordan and Nick are both single and alone, they are "outside of the norm" for the circle; therefore the thing to do is balance the equation.
Daisy does not like to deal with real issues or with reality. She prefers to live in an existence of dolls and make believe where she can create worlds and lives and alter them to her liking in order to avoid the harshness of the real world. This becomes evident almost as soon as she is introduced into the novel, but it especially becomes clear when she tells Nick, in the first chapter, what she said when her daughter was born:
I'm glad it's a girl. And I hope she'll be a fool - that's the best thing a girl can be in this world, a beautiful little fool.
Because of this attitude, creating a romance between Nick and Jordan is nothing more than a pleasantly diverting game for Daisy. Tom does not have the same aversion to reality because he believes he controls his world anyway. A romance between Nick and Jordan is irrelevant to Tom, other than the fact that he likes both Nick and Jordan and sees them as being worthy of his company.