Because they are in the business of gsrnering viewers....and more people watch when she/they are tarted up.
Its not that hard to figure out.
If less people watched when they dressed like that they would stop doing it immediately.
We used to have the TV in the squadron "Ready Room" tuned to the morning news with Jane Pauley. She was nice eye candy, and dressed reasonably.
The briefing office was always met with grumbles when he turned her off to begin the brief for the morning launch.