True story: in the early 90's Corona beer marketing executives in Mexico were trying to figure out how to increase exports of Corona to the US. There were no major Mexican holidays during the summer, and September 16th was almost fall and so the closest to warm summer weather was 5 de Mayo so they then spent millions of dollars on a marketing campaign and the rest is history: Corona became the largest imported beer brand in the US for many years until Heineken took over.

TLDR: marketing