Hacker News Reader

Possibly, but in my experience the less real work there is the more politics and thought leadership tends to crop up.

AirBnB at least seems to keep churning out loads and loads of perhaps marginally-useful open source software https://airbnb.io/projects/

Maybe those engineers keep busy with these hobby projects, and then that makes for good PR to recruit more devs?

Probably not, at least not if the generalized version of Parkinson’s law holds. The demand upon a resource tends to expand to match the supply of the resource (If the price is zero).

TPS reports, probably.