Every derivative is named as Ubuntu, and if you have few of them in one computer all of the are called Ubuntu in the Grub screen, and if you don’t remember, which one is in which partition, you have a problem in booting the right derivative you want at that moment. It is understood that, the base of all derivatives is Ubuntu, but they can be named differently in lsb-release and os-release, so they are correctly shown in the Grub window.
I mean, Kubuntu with KDE has nothing to do with Ubuntu with Gnome for example.
Personally, I change the names those files, so my Grub window shows, Kubuntu, Ubuntu, Xubuntu etc. But, not everyone knows what to change, so how about giving the correct name to the derivatives?