I think with some of them it must be businesses. Like I bet Donut Day was started by a donut company to sell more donuts, and Chocolate Day was probably like Hershey's or something. But Tell the Truth Day? That's more weird so idk how that came about lol
But tomorrow is cow appreciaton day and that one actually does tell me where it comes from: Cow Appreciation Day was the clever brainchild of the Chik-Fil-A company, creating the story of a daring cow to encourage people to skip their favorite burger joint, and come to their local Chik-Fil-A instead.