Why is this the adult Halloween costume equilibrium?

New York Times:

The trend is so pervasive it has been written about by college students in campus newspapers, and Carlos Mencia, the comedian, jokes that Halloween should now be called Dress-Like-a-Whore Day.
. . .
“Decades after the second wave of the women’s movement, you would expect more of a gender-neutral range of costumes,” said Adie Nelson, the author of “The Pink Dragon Is Female: Halloween Costumes and Gender Markers,” an analysis of 469 children’s costumes and how they reinforce traditional gender messages that was published in The Psychology of Women Quarterly in 2000.
. . .
Men’s costumes are generally goofy or grotesque ensembles with “Animal House”-inspired names like Atomic Wedgie and Chug-A-Lug Beer Can. And when they dress up as police officers, firefighters and soldiers, they actually look like people in those professions. The same costumes for women are so tight and low-cut they are better suited for popping out of a cake than outlasting an emergency.

UPDATE: John Tierney's NYT op-ed calls it Slutoween and wonders if it isn't a bad equilibrium, a disarms race:

When I see fundamentalists and feminists jointly denouncing something, my knee-jerk libertarian response is: bring it on! If the stores are stocked with nothing but slutty costumes, this must be what customers want. The market has spoken.

I’ve started to wonder, though, if Halloween is a case of market failure, an arms race that’s out of control.