Not all Linux users use Ubuntu. Especially those of us that want the latest available software, we like to run rolling release distros like Arch Linux, OpenSUSE Tumbleweed, Manjaro, CentOS Stream etc.
Others may like to use Debian or Redhat for thier stability.
Users with low-end hardware might use Puppy Linux, Peppermint, etc.
Releasing in appimage format would mean all of these distros are compatible with your software.