I think you are confusing bug bounty programs with espionage and cyber warfare. The USA definitely accepts vulnerabilities for any system (or at least target systems), paying good money for them if it is an attack chain, giving them that competitive edge you mention. They have at least one military organization over this exact thing (USCYBERCOM) and realistically other orgs to include the intelligence community. There are no bug bounties on "any" system because bug bounties are part of programs to fix bugs, not exploit them. They therefore have bug bounties for their own systems, as those are the ones they would be interested in improving. What you described, which they definitely do, is cyber espionage, and those bugs are submitted through different channels than a bug bounty.