Why do you think gatsby throws such lavish parties, peopled by strangers?

The parties have nothing to do with Gatsby himself. He doesn't care if he attends and usually can't be found. The parties are a statement. They are a way in which he can stage events that will get his name bandied about, all in the pretense of having one woman hear his name. The attention he desires is Daisy's alone. The parties, if she hears of them (he knows that eventually she will), are meant to convey to her that he is now financially worthy, that he can afford the opulence and society she is accustomed to. He wants her to know he's there wild, expensive parties given on a regular basis will generally do the trick.