I dunno, maybe because people pay porn stars to take their clothes off. Everyone else has to do it for free 
+-RH
LOL! My late Uncle used to get Playboy TV, one night it's on in the background while we're shooting the bull and drinking beer. On the screen, their interviewing these ditzy porn chicks at the CES in Vegas about their ideal "date" and what it took to seduce them. It was fairly insipid. Then they went to this hard looking blonde, whose name I can't recall, as this has been nearly 30 years ago. She goes, "Pick up a pizza, give me 1200 bucks, and I'm yours for the night." Uncle Jim yells out, "Finally, an honest porn star!"