I would love to see the latest version of KolourPaint in the ubuntu LTS repositories. The currently latest version of KolourPaint is 17.12.3. This version is so old, it's not even selectable as a version for bug reports.
This is up to them, not us; we don't control and have no input over distro packaging decisions. You might try using the Snap or Flatpak releases instead if you want a newer version of the app but can't leave the LTS.