Remove the unattainable stuff would you? I'm one short and I was 400 minerals short of that one. At least remove their protected status.
I wonder how completion rates are calculated. If SK goes down and is removed, will it cease to count towards it?
This was discussed back when they were removed. The achievements themselves are legacy achievements, and the developers either didn't want to remove them from steam or simply couldn't. They settled for the only option Steam gave them, which was a "hidden" option.
That being said, we have the legacy achievements in-game on our achievement page. I wouldn't be against having them pulled off Steam as long as they're still connected to our knight.