* First you have a few occurrence of the same search query in your search history (because only a few people searched similar words in the past)
* You can't either use synonyms of remove stop words to recommend better content (IT, can means "information technology, or the pronoun. THE can be an acronym, ...).
So basically the only thing you can do is search words. Confluence is worse than that because it tries to remove stop words and do things that break exact match search. But this is a difficult job. Ways to improve search: allow multi titles, index with tags, attributes, only do exact words match, allow users to suggest content for a specific search query, search autocompletion, searching in live during typing ... (many things that Confluence doesn't care about). You also have to respect rights when returning documents, each documents, can have rights from folder or document itself, inherited from team access or user access, so this is really computation intensive too, or pre-compute rights
(Working on a competitor  of Confluence and I have put plenty of hours of work on that specific issue, and I can tell you this is really hard)
Even early Google had more power user features than a typical B2B product search bar.
Boolean expressions (NOT, OR, AND), exact match strings, links-to, linked-from, in-folder/category, etc. should be mandatory for these workflows. Better if you can include search queries as live page content, as in Notion & Height.
Power users are a small share of users of knowledge management software, so it is difficult to build a system only for them. Most people just type a few words and give up if they don't find the result in the 5 first results.
In practice, knowledge management at companies is a specialization. There are <5% of employees that go around and document/organize things for everyone else. Most employees are passively consuming information and information hierarchies built by someone else.
If you're not building tools for those power users, you're not building for creating and organizing content in your system at all.
As an example of how nuts this is, managers at my company regularly try out various search terms, create index documents, and do "internal SEO" to optimize how other employees will discover documents. This isn't a byzantine environment like public web search is, why do I have to hack around the wiki's default notion of page relevance?
My belief is that knowledge management can't exist without power users, which we call "admins", these are the ones responsible to make sure content is well organized for others and create content if necessary. Those people need specific tools to do their job well, which to me is more something that you can have in an admin interface while all the users use the basic interface.
Those tools have two sets of users, admins (curators, creators, organizers) and regular users. We need a different interface for both. And that's exactly what we are working on.
> This isn't a byzantine environment like public web search is, why do I have to hack around the wiki's default notion of page relevance?
That's exactly why I suggested to have multi titles, when you get that and you facilitate the suggestion of new titles for a document, anyone when finding a document can suggest the query terms he used, and that can benefit others users