> I wish I knew how the Googles and Facebooks hire a crowd of junior programmers and have them do these amazing things

Volume. You are forgetting (and/or haven't been privy to) all their failures. Statistically if you do 100 things 1 or 2 of them will be amazing, the rest are crap. We've seen publicly a few of those companies' failures. I'm sure there are many more we haven't.

They haven't managed jr devs any better than the rest of us. They just brute forced it with shed loads of money and people.