There are two reasons why Jay Gatsby no longer throws his famous, elaborate parties in The Great Gatsby by F. Scott Fitzgerald. It is safe to say that he did not enjoy his own parties, since he rarely appeared at them; he must have had a reason for throwing them, then. Jordan tells Nick that, just like Gatsby built his magnificent mansion right across the water from Daisy, he threw his extravagant parties hoping that Daisy would one day attend one of them. She never does.
After Gatsby and Daisy are reunited, Daisy does show up to one of Gatsby's parties by invitation with Tom and Jordan. While Tom loves it because he meets all kinds of women (potential mistresses), Daisy does not enjoy herself. She would prefer to spend time alone with Gatsby, which she manages to do even during the party; the couple sneaks off to Nick's house for a bit. If Daisy had loved his parties, of course Gatsby would continue them; however, since she does not and he already has Daisy (thus he has no need to use the parties to lure her to him), the parties cease.
The other reason the parties stop is connected to this first. Once Daisy starts coming over, Gatsby feels the need for more privacy, and of course he manages that the same way he manages everything else in his life--in a grand fashion. He fires all the servants and discontinues his parties. The beginning of chapter seven says
It was when curiosity about Gatsby was at its highest that the lights in his house failed to go on one Saturday night--and, as obscurely as it had begun, his career as Trimalchio was over.
Cars arrive and find that, for the first time, there is no party at Gatsby's. It takes Nick a while to figure this out, and when he goes over to visit Gatsby, he is met by servants who are not only strangers to him but appear to be anything but actual servants.
What becomes clear is that Gatsby is trying to protect Daisy and their relationship. He tells Nick:
"I wanted somebody who wouldn't gossip. Daisy comes over quite often--in the afternoons."
The new servants are a questionable sort, recommended by Meyer Wolfshiem. Clearly they are involved in some kind of underworld business and are hiding out at Gatsby's house; however, Gatsby does not much care because he has everything he wants: Daisy.
While it can be said that Gatsby threw his parties because he wanted to flaunt his wealth or some other reason, those were only secondary to the illusion he had about reconnecting with Daisy. As soon as he had her, nothing else mattered to him, so the parties stopped.