Why do you think religious festivals are any different from other things you celebrate?
Religious festivals, and other types of celebrations (May Day, Mid-Winter festivals, etc.) are opportunities for people who share in a community to get together and identify like-minded people. Doing the same thing at the same time each year and eating the same food and playing the same games and telling the same stories all serve to provide a sense of security and stability to a group of people. Whether it's a coming of spring or thanksgiving for the autumn harvest, community festivals strengthen identity.
Religious holidays have been a part of cultures since the dawn of written history. Usually they were developed to bring praise to the god/s of the believers, for often different things. Things such as a good harvest, or the return of warm weather. Christmas was originally a celebration of the return of the Sun, as the days start getting longer in about that time of year. Today holidays are not as important as they used to be centuries ago, or even a few decades ago. They have become more secular, today they are more about getting together and socializing. Besides, it makes a good excuse for skipping work.
The objective is enjoyment, those religious celebrations have nothing to do with worshiping God in spirit and truth. John 4:23,24