Sexy Girl Uniforms

On Star Trek, why is it that the "sexy girl" members of crew always had vastly different costumes than the rest of the crew? That must have been a bit awkward when they were handing out uniforms.

Uniform guy: Here's your uniform...yours....yours....here's your uniform.

*hot girl walks up*

Uniform guy: We have a special uniform for you. *eyebrow waggle*

Hot girl: Uh...do I have to wear this?

Uniform guy:  Yes.

Hot girl: It appears to be...a spandex body suit. Can I at least wear something over the top of it?

Uniform guy: No.