Second Sunday of May in the US

Why do they do this? Why not just have a fixed date for these things? Is it so people can use the weekend to celebrate?

	▲	lostlogin an hour ago \| parent \| next [-]
		If it was a fixed day it would end up being a week day a lot of the time. Maybe that doesn’t matter, but it’s nice to have on a weekend. Maybe I’m missing what you mean?
	▲	jolmg an hour ago \| parent \| prev \| next [-]
		For Mother's Day, possibly, but it's not always the case. Thanksgiving is on the 4th Thursday of November.
	▲	Moto7451 2 hours ago \| parent \| prev [-]
		Yes