A very common myth in the US is Cinco de Mayo is a major holiday in Mexico. It is not!!! It is the date of one of the battles in the Mexican Revolution but has no real significance to them. It would be like saying the Battle of Vicksburg in our civil war was to be a major celebration. Celebrating Cinco de Mayo in the US was actually a marketing ploy by the tequila manufacturers to promote business between Christmas and the summer months. Nothing more.
Cinco de Mayo started in SoCal as a bar holiday.. 2 for 1, free nachos etc.
Money making scheme.