I just use pkgsrc from netbsd

Ah right, that doesn’t have binary distribution at all.

Oh wait [1].

[1]: https://www.netbsd.org/docs/pkgsrc/bulk.html

Who besides Joyent and NetBSD would ever do a bulk build?

Portage can also do binary packages. That doesn't mean you have to have them. You can just not ever enable them and be fine.

By that logic, Docker doesn't have to do image distribution either...

In pkgsrc, building packages isn't done by default and 100% optional. I'm not sure what logic you're ascertaining here.

There were operating systems before package managers and AFAICT IIRC the first package manager "repository" was a stack of floppies.

But yes, there's always a choice to be made. Docker could separate out the image repository elsewhere. It could integrate buildroot. It could use a suitable initramfs generator. I'm not sure why present day devs like to create a hodgepodge of different distros mashed together and even do it all from CI, while the same CI could also run gmake on a source tree.

For a sysadmin, docker would be fine. For a programmer, dealing with binary blobs all day, that's IMNSHO not what programming should be about.