Not every country celebrates the hangover day after drinking for Walpurgis night, I'd assume?
Edit because it's a very specific reference to my country:
Here in Estonia we get May 1st off, but we can't really call it International Workers' Day because then we'd also be celebrating oppression and forced labor, as the soviet union was nominally socialist, but in reality quite oppressive. IWD was very important to the soviet union, they held huge military parades (to show you what would happen if some part of the union would cease to be good obedient workers of course).
So instead we get May 1st off for what we call "Spring Day" AKA May Day in other countries. Incidentally it's the day after Walpurgis night, the ancient celebration of witches and shit.
Also the loser country that doesn't celebrate may 1st has had a labor day for longer than IWD has existed, at least in some states (been a federal holiday for like a century too now). It's just in September.