And there weren't any other gay clubs in Philly who had an under-21 night.
It brought and allowed young gay men, who typically wouldn't be allowed because of their age, into the bar, which thereby brought older gays who enjoy looking at, interacting with, hitting on, younger guys. Think about why Woody's used to have the 18+ dance-floor nights on Wednesday. Not necessarily a horrible thing, but they don't have as much invested interest in serving the gay community exclusively anymore, since their clientele has expanded so much.
Woody's is so fucking crowded now because it's basically become a mixed straight bar with a gay past. None of those places allow minors to enter their establishments.