Well XM has always and continues to to show WIP, concepts, and basically everything else possible with their other licenses. Yeah it affects business, you can ask you can beg, but bottom line if they say no and you want the license you gotta. Hell even SS has been revealing their new concept stuff through Disney presentations now ;p
It must have to do with the Lucasfilm side of licensing then, because Marvel falls under the Disney umbrella and they have no problem showing concept art and WIPs for those pieces as you say.
I honestly just don't get what the hold up is.