[alpanka]

You are ignoring that we often use software created by other people.

Raise your hand if you have ever spend an afternoon trying to get someone else's build scripts working. Wondering why make, cmake, scones and ninja are used in the same project...

[calvinmorrison]

There you nailed it. Want a feature X in the plan9 kernel? Okay, add it. Recompile and Run. When a system is self contained and has fewer external users it's easy to iterate and develop without the fear of breakage