I was looking at the Sandbox archive here, and it says at the top, "This question and its answers are locked because the question is off-topic but has historical significance. It is not currently accepting new answers or interactions."
How is the question off-topic for Meta? I just don't understand. It seems perfectly on-topic to me.
The lock was performed for its effects of locking the question and all of its answers, so as to serve as a permanent archive and prevent future modifications. Unfortunately, the only feature that allows for that also has the side effect of labeling the question as off-topic.
At the time the question was locked, the only locking option that allowed locking all of the answers at once along with the question was the historical lock, which labels the question as off-topic (as its original intent is to preserve questions that are not considered on-topic for the site today but were very popular that they should be archived rather than deleted). Other types of locks only lock the question and not the answers, which is not what was wanted here. (Since that question was locked, a new "obsolete" lock was introduced, which has the same effects but instead marks the question as "out of date".)
There is an active feature request for an alternative lock reason wording for meta only, which doesn't label such questions as off-topic. Such a thing would also be useful here.
It is on-topic, but the vast number of answers (and perhaps the unusual formatting in some of them) made it impractical to keep around. That's why staff members created a new Sandbox and moved the existing answers to the question you found. This might happen again in the future, which, given it's a sandbox, is quite acceptable.
