The problem is the base architecture & the current understanding how software works in linux: in the current dominant linux distro design the distros feel responsible for packaging and integrating the software and don't care for ISVs or external compatibility. This distro system is built around the repo, means tight coupling of system and apps, the separation is extremely weak. And this means typically also that the update cycles of the system and apps are synced, means outdated apps as long as the distro don't upgrades or update enforcement on every distro update. Also by sheer number of integrateable apps in a distro system seems to be limited to 10.000s of apps
...beyond that this integrated enourmous blob called repo is not maintainable anymore (for comparison windows ecosystem has millions of apps, android also). This would be maybe standable if we would have only one distro....but we have hundreds multiplying the needless effort, creating a highly incompatible ecosystem. Also, distros are closed circles... if debian decides your software is not in, it is not in, unlike windows where everyone can address windows. So, distros repos are not some kind of app store like android with easy placing of software by arbitrary third parties. As the distros are focussed on their repos the possibility for external software integration is weakly developed. Or, as Ian Murdock summarized it wisely: "the key tenets of open source is decentralization, so if the only solution is to centralize everything, there’s something fundamentally wrong with this picture."
Windows and a platform system decouples system and apps, defining stable interfaces and care for binary long time stability. This gives the easy possibility for arbitrary application development, deployment and updating to third parties... ISVs. This system was proven to work extremely well and ended for windows with a ecosystem of millions of high quality software products with excellent long time compatibility.
The platform provider (MS) cares for the stability of the platform and interfaces, the ISVs cares for updating the apps and rely on the stable platform. On linux, the ISVs can't rely on nothing making it pretty complicated to address "linux" with external binary software like games..
("PPAs", "rolling releases" and "distro hopping" are inconsequent ugly hackish approaches with significant downsides... real solution approaches are "self contained bundles" or "half-rolling release systems", both would also need efforts by the ecosystem ... currently Steam seems to push the distros in this direction)
So, to start with this, looking at http://www.debian.org
/ they've currently 37.500 official packages. It's over the 10k limit you're talking about.
Archlinux provide more than 10k packages in official repos and more than 40k in AUR. Still more. These were two examples
You think rolling release PPAs & co are ugly hackish approaches? Look for example at http://deb.opera.com
/ this is where Opera Software, the editor of the browser with the same name provide a deb repository to users and they can freely use it. Mozilla have their own repository too and I think it can be a good thing.
About rolling release, I tested it on Archlinux, explain why do you think it's a bad approches? For my part I don't think so as you don't have to care about system upgrades anymore : you update regularly and that's all.
About decoupling the distribution and so on : Microsoft as Apple are slowly moving to a totally closed way of distributing apps where you'll only be able to do it through their app store with all the limitations belonging to that choice (some peoples for example some devs on Mac OS are really angry about this and have to remove some features from their apps.
Finally, the approach where apps and every requirements are encapsulized in on package isn't a good idea. Some distros still use it (Slackware) because they use a very old and bad design. Why ? Difficulty about maintainability (if all is centralized in a package manager, it's easier to care about), conflicts, disk space (multiplication of copies of same components means that much more space used) memory management : different copies of same library on disks means that much different copies in memory if you run them.
To be short : it's inefficient. That's one of the reasons why to manage memory and because I used all of these OSs, on the memory management point Linux > Windows > Mac OS (Windows have some common resources that OS X don't have. They package inside their .app more things than Windows in their software folders). So, of course, there are other reasons (swap management for example), but I still tell that, at least for me, it's a bad idea of design (and looking at the choice of most Linux's distros and most BSDs, they've the same opinion).
PS : Slackware is very old and maintained by only one guy. It can an explanation.