In "The Great Gatsby", why do Tom and the sloanes snub Gatsby after asking him to dinner?

The incident occurs when Tom, Sloane, and a young woman were riding horses one afternoon and they stop by Gatsby's house for some refreshment.  They stop mostly because they wanted a rest and something to drink, but also probably because Tom was curious about Gatsby and how and where he lived.  It's clear from the first comment Sloane makes that Sloane sees himself as superior to Gatsby. He is rude in his abrupt comments and in his lack of desire to join in the conversation.  The young woman, after two drinks, opens up some and is more friendly.  She asks Gatsby and Nick to join them.  Sloane does not want any part of that arrangement and whispers something to her.  When Gatsby leaves the room to get ready, the three have left.  Nick understands from the moment they arrived that they are not there because they like Gatsby.  They are simply using him as a pit stop and because Tom wanted to know more about Gatsby since he is suspicious of Daisy's activities and involvement with Gatsby.  The three snub Jay Gatsby because they see him as a nouveau-riche upstart who is beneath them in every sense.  He doesn't have the disinterested demeanor that they, and their crowd, possess. He is too eager to please because he doesn't have the long-standing past of money and all that it brings.  They, along with Daisy, Jordan and others like them, are the careless people that Fitzgerald talks about in the last chapter.