Do you though? Most users just want the latest upstream release, packaged up so they don't have to deal with compiling or dependency management themselves (and have a chance of a clean uninstall), not any extra testing or integration. Hence the popularity of PPAs, Snap/FlatPak, etc..
Recompile, yes. The rest, probably not - upstream usually does that better than any distro. Distro-specific bugs are usually caused by that distro's changes made to "integrate" the package into the distro, which are usually not something the user wants. Again, hence the popularity of PPAs and Snap/FlatPak.
> Fedora often publishes even pre-release versions of some software packages, if you want to talk about "latest" version.
Fedora has the resources to do that because they're managed by a huge company, and they're big enough that upstream will likely make changes to accommodate them. Most distros aren't on that level.
The OS engineers are usually not the ones maintaining Wesnoth, and if they are it's because they want to.
There are separately updatable shared libraries via runtimes, they're just not managed by the OS (on purpose).