Before I was asking a question, I had a look whether it could be off-topic (help). Since I didn't consider it as off-topic from that page, I asked the question.
Quite soon, it received comments to vote it as off-topic, which made me wonder.
Finally, I found that the on-topic help page lists much better reasons for questions to be off-topic. That made me delete my question.
This violates the principle of least astonishment. Is it possible to migrate the off-topic reaons from the on-topic page to the off-topic page?