Nothing ever comes “directly from the developer”, and any developer that attempts to do so ends up in a level of hell not yet documented. There are way too many distros, way too many architectures, way too many moving targets, that also includes iOS, macOS and Windows. No single developer can hit them all. There's no standard packaging either. So, usually they only package for one or a handful of popular distros, or one container format. But that's the magic of FOSS. Anyone can take the source code and repackage it, redistribute it and make it available for others. This is assumed to be a strength and not a weakness of FOSS and Linux. Thus, the distros create their own official repositories where they make themselves responsible that everything will mostly work nicely with one another.

The difference is that package repositories are safe havens of compatibility. While appStores are enforced cages that cannot be escaped. If a package repository tries to fuck up with users, hurt the FOSS space (looking at you Ubuntu Snaps), or gets compromised by a bad actor; you just move to another repository, another distro, a different format, another safe space. If Android or Apple decides to enshittify and fuck over customers, users, get compromised or do something to hurt developers, you are fuck out of luck. This difference matters.