I think it's disingenuous to say tribes and families don't "require much process." The processes are just more implicit than explicit. When you ask your parents for a new toy and they evaluate whether to say 'yes', that's a process - just an informal one. The only reason that's really possible is because the relationships are much more intimate and fewer.
When you start to scale into numbers where it's just infeasible for "everyone to know everyone" then formal processes have to take the place of those informal ones. I can't evaluate Jim's request for 10 additional storage disks informally because I don't know the first thing about Jim.
Coordinating lots of people is really hard. I would guess Airbnb is getting about the size where keeping the culture intact will require a sizable time commitment from the top level. Airbnb keeping that same culture at 20,000 employees would probably be a sociological feat all on its own.