I think Andres explained really well the nuance between why some threads are autoclosed and others are not. And then some categories "go stale" at different speeds. For example, simple r-coding questions can usually be closed quickly, while shiny problems often take a while get sorted (And then things like jobs and gigs close in 1-2 months).
Why auto-close instead of keeping threads open indefinitely? We used to have threads open indefinitely but found that too often follow-up reply-posts were only tangentially related to the original topic. With the goal of keeping things succinct and tidy, we introduced auto-closing.
I also like the idea of it being reasonable to ask an almost identical question every new year, but with the new thread being focused on the latest technologies, resources, and best practices, without being bogged down by all the old, often deprecated discussion.
That motivated the added text "If you have a query related to it or one of the replies, start a new topic and refer back with a link." in the thread-closing message.