That's pretty much standard for
any social network. Facebook, Twitter, Pinterest, Tumblr, they all just have a front page inviting you to join and/or log in. And a not-insignificant chance of flat-out refusing to show you a specific post someone linked to unless you're logged in.
If you scroll down, the default home page will show you a tiny snippet of the timeline - but it only shows the "federated" timeline, made of public toots from every other instance this one knows about, instead of the "local" one of public toots from this instance, which maybe kinda defeats the point of being a sample of what you'll get if you join this particular instance...