On 15 June 2022 we removed the four-day aging out for all spam and rude/abusive flags. We had a recent case were some spam went unhandled and unnoticed on a smaller site so we decided to revisit this request. In doing so, we checked the number of flags that have aged away over the last year and, on most sites, there were none.
Even on the sites where there were some that aged away, the flags were on a tiny number of posts that happened to get multiple flags but not enough to get deleted by users - but the flags were valid.
When talking internally, the only reason we could imagine that we would want to age these out is to avoid a post getting a slow trickle of votes over months (or years) and eventually getting deleted but that wouldn't happen because the mods would handle the flags and if they declined them, the red flags would be cleared. So the only way this would happen is if the mods ignored the flags forever - which isn't happening - or marked the flags as helpful without deleting the post and clearing the flags... which seems really unlikely.
As such, we've decided that there's no harm in removing this setting network-wide. Individual sites have the option to reinstate this but I can't actually imagine why they would... because I'm honestly not sure why we would age out these flags at all.