A lot of Distros could just be scripts run on other mainstream distros, but PopOS, as you have mentioned, has a different release cycle. So it needs different repos, and that could be a little bit hard to maintain as a script.

They also have a separate installer that has features for a better Nvidia experience, which is very hard to pull off as a script (also very hard to pull off in general; because Nvidia).

With the new Cosmic DE and the new tools they've written using a different toolkit, it will be a lot harder to maintain that script, and they may need to make a new flavour of Ubuntu; "Cobuntu", that will not be an official flavour, because it doesn't use snaps.