The purpose of moving a conversation in comments to chat is not suppressing it, but rather moving it to a more suitable place (at least as far as I can tell, this is SE's intention behind the possibility to move a comment thread to chat). However, I quite understand if people feel different about this. Some related discussion (on Math.SE's meta) can be found here. As to the post in question, I undeleted the comments again.

I think it is not even easy to predict whether reducing the number of votes required to close a question would actually lead to questions being closed faster. -- There may also be an opposite effect that makes one more reluctant to vote to close if one's vote has a higher weight. In any case, as long as there is no bigger problem with the current setup, I'd be very careful with such change which may have various hard-to-predict consequences.

@TimCampion Yes, indeed reviving the tag was completely unintentional. I removed it from the question, as I didn't see that the question is about a known open problem / known open problems.

@DmitriPavlov Then maybe I misread the explanations in the Wikipedia article on this. And of course "PhD-level" is not quite a perfect description of what is on-topic here -- but which single word can be such? -- Maybe you have a better suggestion on what to write.

@DmitriPavlov Maybe replacing "graduate-level" by "PhD-level" would make that sentence more universally understandable? -- Or would the meaning then still be unclear in Russia (which, as I understand, has a 2-step PhD system -- Kandidat Nauk / Doktor Nauk)?

@TimCampion Users with >=10k points can vote to undelete a question, and it takes 3 votes to take effect. Posts with recent delete- and undelete votes are shown in the tools here: mathoverflow.net/tools?tab=delete&daterange=last30days (accessible for users with at least 10k points).

Aside from the general question, here the OP has deleted their question after you answered it -- that is rude. Therefore I undeleted the question.

I think the reason for the downvotes on and closure of your question "Understanding the mechanics behind the Riemann hypothesis" is just that -- as opposed to concrete questions which can plausibly be answered here -- posts in blog-like format are not really well-suited for this site. -- While (being a group theorist and not an analytical number theorist), I cannot comment on the mathematical contents of your post, please don't take the reactions of the community as discouragement to further contribute to this site!

What I noticed is that there is a steady stream of questions with no positive and no negative feedback which after a year fall victim to auto-deletion, in a part of the cases likely just due to inappropriate tagging. -- I sometimes went through the list of such questions to see which of them could be improved and should be brought back to attention, and edited and sometimes upvoted them.

As to my experience with reviewing -- there are not much surprising things to be said in general. I didn't make a statistics -- but as likely everyone would expect, a part of the posts appearing in the review queues is good as they are, another part of the posts are good after some polishing or clarification, and yet another part cannot be rescued (e.g. calculus homework, and sometimes spam). Over the years I became more careful with my judgments as to which questions can perhaps still be 'repaired' and be made on-topic, and which really cannot.