It's private because the mods and the community cannot handle the sudden interest. (A subreddit squeeze!)
They even say this on the placeholder page.
A few hours ago zjz (a mod) posted about trying to get an unlimited API endpoint for Reddit from the admins so the mod bots can cope with the load.
"We are experiencing technical difficulties based on unprecedented scale as a result of the newfound interest in WSB. We are unable to ensure Reddit's content policy and the WSB rules are enforceable without a technology platform that can support automation of this enforcement. WSB will be back."