Victorian Girlie

The Lady of Shalott (1888) by the British painter John William Waterhouse (1849-1917). The Lady of Shalott" is a Victorian ballad by the English poet Alfred, Lord Tennyson (1809–1892) and tells the story of a noble Lady and her tragic love to the Arthurian knight Sir Lancelot.
Like many of these  Arthurian legends the subject was especially popular amongst the Pre-Raphaelites who did various paintings.
Nevertheless I don't understand why Waterhouse is often called himself a Pre-Raphaelite. He had absolutely no relation to them and exploited only the popular subjects in a cheap way.