Valve keeping up with the trend of "worst kept secrets". You need an invite to join the alpha but since everyone who owns it can refer their friends, it spread very quickly.
I've been playing it the past few days and it's honestly very fun. Still a bit rough around the edges (especially in terms of balance) since it's in early access, but it has serious potential to be dota 2 levels of popular.
For the unaware, Deadlock is a 3rd person shooter MOBA. It feels like a mix of Dota and Overwatch/Team Fortress. Nobody is allowed to share footage or screenshots, but obviously with so many playing there's a ton of leaks out there.
Valve keeping up with the trend of "worst kept secrets"
Well it's very intentional I believe. You can invite an unlimited number of friends and there's no NDA or anything, they just casually ask you to not share details about the game since it's still a work in progress and in alpha, despite it looking like mostly finished to be fair. Characters are fully voiced and nothing really screams placeholder content, and most updates are regarding "balancing" and mechanic changes, just trying out what's best.