Different material that's being printed on, printing method, and lighting between the two. Even the raw images are somewhere between those two, with it being slightly pink.
And since these being serigraphs means they have to layer the colors and with that, they have to layer the colors in a way to make sure they're as close as possible. Take a look at the WoM poster. Notice how there's a outline around the orange? Side effect of a serigraph. Who knows, if they printed this like a normal poster it could've been brighter?