They also a have ton of licensees which are AAA game studios with qualified profesionals often backporting fixes and features into the main branch. Appart from

They also a have ton of licensees which are AAA game studios with qualified profesionals often backporting fixes and features into the main branch. Appart from that the engine is completely open sourced. I also get the impression Tim Sweeney, the one man developer behind the first engine, is rather good at assembling and managing tech teams.