why do people give party favors?!
Because you got them a present so they give you a gift to thank them for coming!
If you are having a birthday party, you need to buy favors for your guests. It is a great tradition that shows you appreciate your guests' attendance and want to thank them for helping celebrate your big day. It may be considered rude to not express some appreciation after everyone devoted their time to you.
Birthday party favors can be traced back to wedding party favors. They are small appreciation tokens to express gratitude for guests' attendance. Today, favors are given at many children's birthday parties as thanks from the host. This Western tradition has also spread to many other countries.
Obviously, to thank the person or people for taking time out of their busy schedules to share with you & your festivities.