Why isn’t Labor Day in May?

(Dictionary.com) In more than 80 countries, on May 1, labor unions and working people take to the streets. The holiday is often referred to as International Workers’ Day or May Day.
The day marks the 1886 Haymarket Affair in Chicago, where police shot and killed several demonstrators who were fighting for the eight-hour workday. Over the next several years, people across the globe began demonstrating on May 1, and in many countries the day became an official holiday. Continued