Why does everyone else celebrate labor day on May 1 and not on labor day ?

In 1884 the AFL declared a general strike for the 8 hour day for May 1 1886. The socialist international noticed that socialism was not taking off in the USA so all their international this and that days are based on US events. The big one -- international labor day is May 1.

So why did the AFL hold a strike May 1 and not on labor day ? Once I told a former student of mine that labor day was already a holiday in the US, so a strike would have had little impact.
Here I admit that I was wrong see