Well someone at some point requested a search function, maybe a business owner in house or a customer, but regardless they said "no problem fam" and hastily hacked together the monstrosity they've built.
What I'd preferred was if they took the time to implement it correctly from the get go. What they built instead is of no use to anyone. It's a search function in name, but it doesn't provide useful search results.
Search is hard though. From how it's behaving I think they're just sticking the data in Elasticsearch or Lucene or some such, without having done the long and arduous effort of then making it good.
Though my point is that even though confluence has a search function so broken they effectively don't have a search function, they aren't meaningfully bleeding customers over it. Business sales are incredibly sticky that way. Regardless of what pleases me as a user, Atlassian has no real incentive to fix the problem, and evidently hasn't (at least last I checked).