The cost isn't negligible. The OS team at Apple is smaller than you'd think and has a tight schedule that cannot ever miss a ship date. Basically anything that uses anyone's attention has to be important.

> there's the question of who's going to make the call the not update a certification that's negligible within the scope of macOS development.

And one way that's managed is to have a DRI system which (ideally) prevents this from happening.