Besides attractivenesses has nothing to do with it.
It's about security.
The half naked "alien babe" is almost always running from something five steps behind her that will most certainly kill her, and then there's this hero in a Starfleet Uniform unloading the full reserve of a phaser compression rifle into this terminal threat, that's probably already eaten her friends and family, till it's dead.
Whosoever that person is holding that rifle, saving the day, is momentarily the most sexiest person in the universe.
That is after all why Kes warmed Neelix's bed for 2 years.