[middleman90]

I like to think that this things are made for the public opinion. More people are exited, easier is for NASA to find the money necessary

[DanielStraight]

They tell you why they were made:

"NASA originally commissioned these posters for an exhibit at the Kennedy Space Center Visitor's Complex in 2009. As part of our Journey to Mars, these versions are now available to everyone online."

They're just freeing up the design of their decorations in case other people like them and want to use them.