I don't know if you are searching "wrong".
Quite often people don't know that there are different search options depending on where they are in the site.
It's sort of a balance. We like
perennial threads. But also, often new threads have new ways of asking old questions that are more "modern" than 5 years ago. So Google is going to love that
thread more. An example of me shamelessly milking google love by starting a new thread on a topic we have talked about in many threads before, but using the words that are trending right now:
https://permies.com/t/163334/permaculture-home-care-cleaning/purity/stink-removing-perfume-smells-clothes
...
I don't fully know how the design is set up, but basically, it's guiding behaviour. With help forums, quite often they have "maybe this thread will answer your question" based on the subject line. It does a sort of search for you because people in help forums are sick of getting the same 4 questions repeated 12 times a day.
On permies, this isn't such a problem. and if it is, the moderators have tools for merging and sculpting threads to meet our goals for this site. That's why the similar threads is based on the body of the post and comes up after the post is finished - it guides the behaviour in the way we are trying to encourage.
I don't know if that makes sense, my brain is par-boiled in the heatwave today.