Every listing site solves the same half of the problem. Time Out, Eventbrite, Dice - they all tell you what's happening. None of them tell you which of your friends would be up for it. And that's usually the bit that decides whether you actually go.
A mediocre gig with your mates is a great night. A brilliant exhibition on your own when you'd rather have company is just fine. Whether you go depends more on who else is interested than what the event is.
Right now that information is invisible. Your friends are seeing events, having opinions, saying nothing. You're doing the same. Everyone's interested in stuff. Nobody knows what anyone else fancies.
So every event becomes a private guessing game. Would anyone be into this? Is it worth sending? Who should I ask? Most of the time you just leave it.
In a CouldWe group, when you're browsing events, you can already see who's interested. Some things have social momentum before anyone's made a plan. You're not just looking at what's on - you're seeing what already has people behind it.