zig build
Furthermore, C and C++ code can participate in the Zig package ecosystem. For example, here is ffmpeg packaged for consumption by a Zig project:https://github.com/andrewrk/ffmpeg
Why not use a system package? Well, because the user's system might not have such a package. They might be on Windows, for example. Or their package might be out of date. [Or the system might have chosen sides in a nasty fork war](http://blog.pkh.me/p/13-the-ffmpeg-libav-situation.html).
So, while system packages are nice for end users, they might not always satisfy the needs of upstream application developers.