Context:
Reproducible builds ensure software can be rebuilt in an identical, bit-for-bit manner anywhere at any time using the same tools. This means that someone rebuilding the software from the same source code will get exactly the same results.
Why is this important? Because it’s a crucial aspect for supply-chain security.
Source: https://news.opensuse.org/2025/02/18/rbos-project-hits-milestone/
I believe it’s less about the packaging system and more about the build system. You’re building source code from thousands of individual projects, getting a reproducible output is difficult if, for example, some library embeds the build date/time in its output.