I visit the private beta login page:
So I follow the link, and click "Visit the site now":
And now I can login:
Is there any reason for this roundabout route to login? Surely knowing the URL of the site should be enough?
It's not pointless. While it does appear to be bolted-on (and it is), it's not pointless.
The main purpose: people often arrive late to things, and when it comes to proposals, we really need those people. Having it is mostly for usability, and it serves two important scenarios:
I know I committed to this darn thing but dangit I can't remember what email I used, I'll come back to this later (and they never come back)
I wish I saw this in time to commit! I'm an expert in transmugated tribble fat rendering to biolithium and the crystallization process! Well, I guess I'll see how the site does in a few weeks (and they never come back, or come back way after crucial decisions were made without them)
It lets folks in that want to get in and do stuff, while giving folks that have taken a keen interest in how new sites come together (or just want to watch prior to contributing) to join more or less as a spectator.
The answer by Energy Numbers is spot on, as is Jay's where he asserts that the effort and knowledge needed to use it is still a pretty effective gate into a private beta. If you didn't commit to it, we need to make sure you at least see the proposal before being allowed to join.
I'm declining this because the use cases are far too valuable to ditch it.
Surely there is a very useful benefit to this roundabout system, isn't there?
The private beta is a fragile but crucial time in a site's development, setting the culture, the mood, the level and the scope of the site.
This roundabout way ensures that not just anyone can walk in and start doing whatever they want. It allows people who know and understand how Stack Exchange works, to find their way in, if they really want to. And keeps anyone else out, unless they were part of the commitment phase.
It's a bit of a weird way to do it, but it does it well.
So I'd argue against this feature request. As the VP of Community Growth Jaydles has explained, the current functionality has a purpose, and it works.