In the really large server-side systems we're talking about here (banks, defense, etc.) both developer productivity and maximum speed rank way, way below other factors, such as having long-lived processes.
Java's not a clusterfuck? I'll take the clusterfuck that's not controlled by a creepy asshole who thinks the NSA is essential and says stupid shit like "Who's ever heard of government misusing information?"
Every potential performance gain C++ might have is completely negated by having to touch that complete clusterfuck of a language.