The developer will often have more tools at their disposal than the typical builder.
Extra tools may be difficult to install or time-consuming to run.
Some files change over time, but are not specific to the build environment. They can safely be generated at distribution time.
Typically, some files are therefore generated by the developer and distributed with the package. Examples include
Documentation transformation tools can be difficult to install correctly with many pre-requisites.
Support tools not available everywhere. Can be time-consuming and the result is not machine specific.
These are changing files but remain fixed for each official release.