I'm pretty sure some topics are just outright muted to prevent abuse (not that it's a bad thing). For example, if you were on /new over the past 6 months, it w

I'm pretty sure some topics are just outright muted to prevent abuse (not that it's a bad thing). For example, if you were on /new over the past 6 months, it was extremely common to see a "Twitter"-titled article get 20+ upvotes and never see the frontpage. People were outright obsessing over Twitter, posting everything they could find, no matter how benign or uninteresting it's content was. Locking the topic until verifiably interesting things happen was a great solution. It probably works similarly for other keywords, too.