Why do Mexicans wear mustaches?

Answer 1

Many of them do, but it is not a special or definitive trait of all Mexicans. Such belief is known as a stereotype, like that one stating that most Frenchmen wear a blue beret over their heads.

Answer 2

Genetics. Mexicans have within their genes a combination of 53% of Caucasian genes and 47% of Native American genes. The combination of both result in thicker, darker and more abundant hair.

Answer 3

Genetics. Most Mexicans have a 50/50 of genes from Native Americans and White Europeans.