The hottest topics are both the most discussed and the most "consistently suppressed", as you put it. That sounds like an oxymoron, but it's just what happens when you have 10x more submissions than front page slots. Frontpage space is the scarcest resource on HN: https://hn.algolia.com/?dateRange=all&page=0&prefix=true&que....
Because of this scarcity, everyone who feels strongly about a story feels that their story is being unfairly suppressed on HN, no matter how much coverage it's actually receiving relative to other topics. You seem to feel that Chinese political stories are being unfairly suppressed for who knows what reason—but there are at least as many users (probably many more) who feel that those stories are overrepresented and that HN is going downhill because of it. There's an email in the inbox right now saying so.
The actual moderation principles we use about all this are simple and have been the same for many years. Here they are: HN is a site for intellectual curiosity, so follow-up stories that don't add new information are mostly off topic, as are riler-uppers that don't gratify curiosity so much as stir up indignation and flamewar. When there have been a lot of stories about X lately, the bar for X stories gets raised; HN readers don't like it when the front page has a lot of stuff they've seen already. That's about it. The execution has a lot of subtleties, of course, but those principles fully explain what you're observing.