Because it's so much cooler to say than, "May the fourth be with you."
But. Did you know that most people in Mexico do not celebrate Cinco de Mayo? It's mainly celebrated in the state of Puebla and the United States. It is not Mexico's Independence Day. It is the celebration of an unlikely victory over the French army in the Battle of Puebla.
Or.
Just a really good excuse to have guacamole and cerveza mas fina con buenos amigos.
