Last night I went to the Ballet Folklorico for the first time. The violins were out of tune there too, just like they are everywhere else I've heard in Mexico. Throughout the two-hour performance I kept trying to decide if this was done to be "authentic," or if for some reason in Mexico any two given violins are incapable of being in tune with one another. I could not decide.
One expert offers an explanation:
"Stanford (1984)...stresses the devastating effect the inclusion of the trumpet initially had on traditional ensembles, particularly in causing the role of the violin to atrophy. According to Stanford, the violin players in the first modern mariachi groups (after the inclusion of the trumpet) subsequently viewed their instrument as less important, and began to play out of tune and with less care. In small mariachi ensembles, the violin was retained only to complete the overall visual image."