Because he wanted to be just like Late Night With David Letterman regular Larry "Bud" Melman.
"He mentioned he always saw Larry [walk on] with those gorgeous models," Letterman's longtime bandleader, Paul Shaffer, told Chicago Sun-Times reporter Dave Hoekstra in November 2009 while promoting his memoir, We'll Be Here for the Rest of Our Lives, cowritten with David Ritz. "Dylan said, 'Why is he with those chicks?'"
Two decades after first appearing on NBC's Late Night—Dylan also performed on the penultimate episode of Letterman's next venture, CBS's Late Show, in May 2015—the singer-songwriter was given the chance to emulate his hero. Well, almost—Adriana Lima is the only model, gorgeous or otherwise, who shows up in Dylan's ad for Victoria's Secret.
There are legends, and then there are legends. Advantage: Larry "Bud" Melman.