TLDR: A lot.
Some packages not providing their commandlines to run the software or having very poor example documentation in -h, or none at all.
The sheer amount of failures that every single one of the core functionalities from boot, init, filesystem, display, userland, hardware, drivers, security have if you're a multi-year multi-distro power user, or even just a simple gamer or streamer.
The instability and corruptibility in all of, including the atomic/immutable, distros on simple configuration changes or updates from the standard package repositories. Even containerization systems like Flatpak, Snap, AppArmor, AppImg, Toolbox, some virtualization, can often all still access and corrupt ample swaths of critical system functionality/operations/storage, user data, or other privileged or sensitive applications and buses.
The wider support of slower, more poorly designed, less stable, less secure distros and desktop environments