Bear in mind, the full text search option was only just brought in on the latest update, and even then only as an opt-in system. It could be they will tweak it later.
For context, on Twitter trolls misused the search system to find victims, Mastodon deliberately restricted how search would work (originally all searches were by hashtag).
If you're comfortable using github, you can vote for URLs to be searchable by giving thumbs up at: