I understand what you mean, but it's a tough one. We tried suggesting users to follow on sign up, but it introduces a lot of bias and centralizes the following. Until now, we just have an empty feed and suggested they peruse global, but you'd be surprised how every point of friction can keep an otherwise good user from figuring out what the site is all about. Once someone follows a user or tag, the badged part of their feed is greatly reduced, yet we think it currently represents a good place to start.
It might not play out that way of course, but we really feel like there was room for improvement in the sign up flow.