Where are you looking on ao3? There are over 273,000 spn works there. Many are destiel, but even if you take out the two most popular ships (Dean/Cas and Sam/Dean) there are over 100k! And enough of those were posted or updated today that it’s more than the first page of search results, so it’s not like they were all posted years ago. Here is the Supernatural tag with those two ships excluded:

https://archiveofourown.org/works?work_search%5Bsort_column%5D=revised_at&work_search%5Bother_tag_names%5D=&exclude_work_search%5Brelationship_ids%5D%5B%5D=5672&exclude_work_search%5Brelationship_ids%5D%5B%5D=35&work_search%5Bexcluded_tag_names%5D=&work_search%5Bcrossover%5D=&work_search%5Bcomplete%5D=&work_search%5Bwords_from%5D=&work_search%5Bwords_to%5D=&work_search%5Bdate_from%5D=&work_search%5Bdate_to%5D=&work_search%5Bquery%5D=&work_search%5Blanguage_id%5D=&commit=Sort+and+Filter&tag_id=Supernatural+%28TV+2005%29