Marc Platt had such a thankless role

I had never heard of Marc Platt before,but once he came onscreen he almost stole the first part of the film.Not only a great dancer but also able to project a winning personality onscreen.For a while I thought he would even be Rita Hayworth's love interest,but unfortunately that was not to be.Instead,he becomes the lover passed over for another, and becomes a sullen,unpleasant presence for most of the rest of the film.One Dreads his subsequent appearances.The wonderful second dance number with Rita does not cancel out the sourness of his character outside the musical numbers.Not a good way to promote a new talent to say the least.Why didn't they just have him fall for Janet Blair right away,and become the standard second couple?An unfortunate choice by the screenwriter,which did little to further Marc Platt's career.