There is a real historical reason why Cinco De Mayo is celebrated by Mexican-Americans and not much in Mexico. This article explains it.
Rooted in Mexico, Cinco de Mayo Flowered in the U.S. | RealClearPolitics
From the article:
It’s Cinco de Mayo, a holiday that originates with an 1862 Mexican military victory in the city of Puebla. The battle pitted Mexican Army defenders against a French expeditionary force dispatched to Mexico by Napoleon III. The outcome was not strategically important -- and the French captured the town a year later -- but it was highly symbolic to the Mexican diaspora in North America, most especially expatriates living in California.
When Spanish-language papers relayed word of the victory to Mexican miners laboring in the Mother Lode country 1,500 miles away, celebrations ensued with fireworks and fiery speeches. In Los Angeles, Mexican-American politicians who’d changed their citizenship without changing their addresses gave patriotic speeches.
California had been admitted to the Union in 1850 as a free state, and the context of the Cinco de Mayo celebrations was the Civil War between North and South. The anti-slavery movement in California had been an alliance of Northern immigrants and local Latinos, and the Battle of Puebla was as emotionally significant to them as the Battle of Bull Run was to Americans living in the East.
(snip)
As UCLA professor David E. Hayes-Bautista has noted, this raised an obvious question: “Why is it that Latinos in the United States celebrate Cinco de Mayo so intensely, when it is not celebrated in Mexico?”
The answer, he says, is simple: “Cinco de Mayo is not a Mexican holiday -- it is an American Civil War holiday, created spontaneously by Mexicans and Latinos living in California who supported the fragile cause of defending freedom and democracy during the first years of that bloody war between the states.”
Kind of cool now that you know the history, isn't it?