The API is much more limited for kernel mode, because Microsoft doesn't want to make it easy to crash the kernel. So it's not just a matter of taking old DOS code and making Windows run it in an old compatibility layer, but actually requires translating the whole thing into a much more limited set of commands to properly draw the graphics and respond to user input.

It's impressive like being able to play the French horn without using the valves, or painting beautiful pictures using only a mechanical typewriter. It's being able to do something that is trivially easy with normal tools, but with such a limited toolset that the accomplishment itself is impressive.