Not to mention the fact that they're all too busy doing paperwork and trying not to get sued by pseudo-middle class, middle aged Daily Mail readers who finger their cunts everytime they hear of a celebrity wearing the same dress twice.
/rant.
Seriously though, Banksy artwork is just a fad, notice how equally illegal, similar street art from other artists is simply removed, as opposed to being bought by people with more money then sense.
...and with that post, people of Britain were so surprised that "tea was spilled, crumpets were dropped and monocles everywhere popped out in shock."