Hey,
Sorry for taking a bit to get back. The short answer is that our search needs a lot of work! We know there are shortcomings with how tagging, keywords, and title matches are balanced. Generally for topic searches like "fishing" we try to encourage people to use tags, and point people to the browse pages.
From what we've seen, the average user using search is trying to find something specific by name, so we optimize for that. The secondary use is trying to find something by topic, eg they want to find games about zombies, fishing, space, etc. In those scenarios we try to point them to our browse pages where there's much more control over how things are filtered and sorted. (for example, if you search fishing you'll see a link to the Fishing tag on the top)
In the long term we hope to update our search system and introduce some of the additional options that are available in browse as well.
There are a lot of games on itch.io, and it's a challenge making sure search returns what a user wants. I know every developer wants to have their game show up first when something related to their project is typed in, but there are too many games to give that to everyone. To handle this we try to give a more organized way for people to get their game indexed through our tags system. The best way to boost visibility on our platform's main site is by correctly tagging your project, filling out metadata, and doing things like posting devlogs.
Hope that helps.