Why

Nixpkgs is a gargantuan codebase. The treewide pattern-match patches happen a lot there. They just need to do the treewide changes, they do the treewide changes despite it can break a lot of unknown things in unknown places. And because classic interpreter does not have a solid type system, it is impossible to check for errors made NOR during making a patch NOR during PR & merge process. Only posteriorly the Hydra rebuilds stuff, and some failed builds get exposed, then people use the stuff and encounter bugs. https://discourse.nixos.org/t/avoiding-targets-of-past-treewide-fixes/5494/5