1 out of 4 question are being closed for being off topic. The majority of them are not closed by the community but by a moderator. Could the community be allowed to help close questions? Could a disclaimer be used instead of closing questions dealing with personal questions?
As with all SE sites, we get fewer closed questions when users read the help section and understand site requirements before posting. In particular, the section entitled What topics can I ask about here should be read and understood.
The community does close questions fairly regularly. Since a single moderator vote will close a question while it takes 5 non-moderator votes, it's natural that many questions end up being closed by mods. I actually let many questions I think probably need to be closed to remain open so I can see what the community thinks. The exception to that is questions requesting medical advice. I close those instantly because the community has long agreed that such questions shouldn't be allowed (and shouldn't be answered either).
We already have a disclaimer. Nonetheless, allowing medical advice questions isn't going to happen. That's an old debate that goes back to the founding of the site and it has always been widely agreed upon by the community. Please read this meta thread. If you want to get medical advice from anonymous strangers with unknown or non-existent qualifications, there is no shortage of sites on the internet where that can be found, but the community here has long agreed this isn't going to be one of them.
I'm not quite sure why you added the link in your question. It's from the very early days of the site when the scope was less rigorous, but even then it clearly stated that medical advice questions were off topic.
Closing a question is not a bad thing if it is a bad question.
Closing a question is not permanent: closed questions can be reopened if they are improved.
Closing a question is to prevent answers before a question is improved.
Not closing a question requesting personal medical advice is dangerous, because that allows it to be answered, and may require the moderators to then delete answers that are inappropriately providing medical advice. Even worse, those answers are most likely to come from people who are not regulars on this stack (because they do not understand the prohibition against personal advice) which makes them even more likely to be dangerous.
Some relevant posts about close-voting on the main meta that discuss the purpose of closing questions and recommend immediate rather than patient use of the close vote: