Although why you would not like or want the latest stable or your app, for example, is beyond me. It's a stable version, you should want the new features.
Call me an old man. But I like when things are stable. I don't like starting my computer, and the software was updated to a new version, and some features disappeared or changed in behavior. This is why I hate the web where people update software right under my nose! With no control from my side.
These repo contains thousands of orphan packages which are not maintained and will never get any update ever again
(proceed to show a list of obscure go modules)
You get the duplicated work of maintainers, packaging the same app, multiple times, for multiple supported version of the distro.
First, the work is not often duplicated. The first maintainer to package will usually upstream patches which make packaging easy. Packagers will look how other distros packagers packaged the app they're trying to package.
Also the duplication only happen a few time. Ubuntu just pulled almost all of their packages from Debian Sid. Same with RHEL/CentOS and Fedora. And so on, and so on
Also you're overestimating how hard packaging is, most of the time, it's scripted. (golang modules in debian, are imported in an almost fully automated way)
You know what distros bring?
Security. (My packages were vetted by packagers)
Uniformity. (All my software works coherently)
Stability. (My software doesn't break at the will of some third party developer)