Check out this social analysis of a pack of wolves: https://youtu.be/d36MK94POaI?t=8m50s

Omegas are the ones gaining from relieving group tension. They do it through play. When extrapolated to humans, tension is usually diffused by making people laugh. Everyone is equal in joy or sadness. Trying to invoke sadness or fear will never work as an omega, making laughter and joy their last hope. This is why the loser of the group will tend to take on the fool's role. Humor is the defense of the weak. It's their way of diffusing tension and distracting attention.

Notice also how omegas are prone to diffuse tension and appeasement. In terms of seduction, tension is one of the crucial elements. Due to their innate incompetence of handling tension, their chances at sex are further reduced.

Now of course this is a highlighted example of the use of humor, and humor in itself is a crucial trait for anyone who aims to be a socially skilled human being. It is however a good look into why the initial sexual attraction is untouched by it. As we all experienced by now, raw sexual attraction emerges from dominant (alpha) traits. Relationships are where humor will score you points though, but that stage is only an option to those who passed the first test.

Summary: Don't fail the attraction test. Use the right traits at the right time.