Fun fact: Nazi Germany insisted on a name change from the fighting day of the workers movement ("Kampftag der Arbeiterbewegung") to the day of national work ("Tag der nationalen Arbeit"). Notice the shift in focus from the worker to the work.

The 1st of May is international _workers_ day. So why is it so often referred to in English as Labour day, emphasising work rather than people?

I honestly don't know, but I think it should be called what it is.

Workers. Not work.