[matthewvincent]

As a resident of Oakland CA, easily one of the graffiti capitals of the world, my take on this is a pretty simple one. Super aggressive buffing campaigns by the city.

Businesses on Broadway in Oakland will actually be fined if they don't paint over new graffiti in a timely matter. When a writer knows he will be buffed over within days if not hours he will probably look for more low key spots that will last longer and actually be seen by peers.

Anecdotally it also seems like there are way more legal walls around town now. Spots where businesses pay the better street artists to do big murals that less established writers won't write over.