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You're raising absolutely valid point about project management but it's a bit of a separate issue.
A project like Matrix or OpenSSL is not only code but also issue management, project management, security, documentation, user support, website, business logic maintenance & updates etc etc. Projects like Nmap, Nessus or Suricata also require very frequent rule updates. All that tends to be extremely boring and routine work.
Volunteers tend to lose interest in these.