Why did Jabba the Hutt force Princess Leia to wear a bikini and why did he keep her on a leash?

When Jabba captured Princess Leia in Return of the Jedi, instead of sending her to the dungeon, what was his purpose for putting her on a leash and dressing her in a bikini? Why did he want this for Leia instead of giving her the same treatment as the rest of her friends?