Why did Banksy graffiti?

Besides being political, provocative, rather large and of course brilliant, his art was placed in highly visible places. Even though he is 'anonymous', I'm sure he's done some effective P.R.( besides stenciling public spaces) in the way of press releases, website promotion, resumes and such.Since Banksy made the lifesize stencil famous (even though he ripped off his Rat image from an older French artist without crediting him) no one can stencil their town without now being said to have been influenced by the famous Banksy. Actually,after seeing the work of Banksy, I will no longer try to fool myself into thinking I was ever a clever artist. So I have stopped making art and now spend my free time on "4Chan" and "/b/", now that's art!