And May Day in U.S. was supplanted by Law Day ("to celebrate the rule of law") but it didn't take off because it wasn't a public holiday.

Ya can't make this up any better.

As a US-ian I can tell you this propaganda works. I grew up not knowing shit about May Day (that's like flowers in a basket, right?) or Labor Day and I routinely confused Labor Day and Veterans Day. This coming from a solidly LIB-slash-Non-Political household of teacher parents.