About 2-3 months ago they basically nuked Youtube's search and recommendation. This was associated with some bad press about those features coming up with "harmful content" like unapproved radical politics & conspiracy theories. Now you basically see mostly curated front-page stuff plus some user stuff that had probably never come up in search before (e.g. a fairly common search term will come up with videos that are a decade old and only have 5k views). Maybe changes in Google search are related?