A poor package repository is a consequence of too many packaging formats, and lack of volunteer maintainers, though (I, too, could have made more to help). So coming up with package formats all the time - .deb, .rpm, .apk, Alpine's pm format, pkg, .dmg, flatpack, snap, docker and whatnot - is exactly the problem (cf. https://xkcd.com/927/). Maybe Slackware got it right after all by only building from upstream .tgz source archives. We'll see in a decade or two what software is even remotely in a usable state still.

If it was just about packaging, everyone would just have a build server that creates their binary once and then slams it through https://github.com/jordansissel/fpm.

But there are more fundamental differences between OSes than how the insides of their packages look. The packages are "differently shaped" to prevent you doing something stupid and damaging your OS by installing a package that will spew files in all the wrong places, and rely on classes of protections that aren't there.