Some people don't like a blank space, so give in to the urge to fill it. In Northern Ireland, blank walls are used to promote political messages. Personally, I think it's vulgar in public, but I should enjoy having a mural on my sitting room wall....a nice woodland scene would be very relaxing.
There is a distinct difference between mindless graffiti and art. Just one of many examples to be found the world over.
Is that a house in the French Quarters of New Orleans? Of course first and only time I was there was in 1970 and PG with second kid. It was not a pleasant time, I do recall they loved graffiti.