Sad to say, as many have mentioned, social life (not just clubs) take disposable income which many millennials do not have to spare.
70-80 bucks to go out doesn't seem like much to professionals, but for someone with a part-time gig, a roommate, and 60K in loans, it is a lot.
Add to the fact that social media has made most women entitled Femic*nts, it is difficult for a brehs to approach without being considered creepy or violating her space (unless you are [insert Hollywood celeb])...
The larger issue is that real-life social interaction has been curtailed for young millennials in favor of emoticons....