In the world of West-European Megalopolis art and cultural heritage are the equivalent of power.
And these historical megastates do anything in their power to hoard as much cultural assets as they can. Museums have become the new Forts.
Now ain't it annoying that a particularly motivated group of art thieves wants to break all of this art free into the public?
[1]: Dreams of Blauw are any form of crystallised thought based on honest expression. Sometimes they linger a shade of blue in your after-image.