Why did Lavan make a party for the men of Charan before the wedding?
Da'as Zekenim, Hadar Zekenim: He wanted to get Yakov drunk, so he would not distinguish Leah from Rachel. This is why he did not make a party for Rachel!
Tosfos ha'Shalem (2, from Bereishis Rabah 7-:17): He told the men that he would trick Yakov into remaining another seven years. They liked the idea. So he took securities from them not to reveal the ruse, and did not return them. The party was from their money! 4: Oznayim la'Torah #1: So that the people of the town would would assist him to trick Yakov by switching Le'ah for Rachel. 2
Oznayim la'Torah #2: In order to be able to subsequently tell Yakov that he did not give him Rachel because the townspeople would not let him.