The point being that this very short list of options is extremely thoroughly-worked-out, which is a level simply not available today in a stock Ubuntu distro and its themes. I can choose elementary, or Mint, bitbthat is essentially an OS distro level decision. I can download some themes, but its not interchangeable at will, and the depth of implementation of gnome or kde themes is very shallow.
I expect that to truly do this would require not just graphical styling but also switching lots of packages around (eg a file manager). Maybe the path there looks like a giant Nix config to capture all the dependencies?